diff --git a/Cargo.toml b/Cargo.toml
index dd55452a..67b27efd 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -40,6 +40,7 @@ bundler = ["dashmap", "sourcemap", "rayon"]
 cli = ["atty", "clap", "serde_json", "browserslist", "jemallocator"]
 grid = []
 jsonschema = ["schemars", "serde", "parcel_selectors/jsonschema"]
+level6 = []
 nodejs = ["dep:serde"]
 serde = ["dep:serde", "smallvec/serde", "cssparser/serde", "parcel_selectors/serde", "into_owned"]
 sourcemap = ["parcel_sourcemap"]
diff --git a/README.md b/README.md
index f44d7b3c..484616c2 100644
--- a/README.md
+++ b/README.md
@@ -28,8 +28,11 @@ An extremely fast CSS parser, transformer, and minifier written in Rust. Use it
   - CSS Nesting
   - Custom media queries (draft spec)
   - Logical properties
+  * [Color Level 6](https://drafts.csswg.org/css-color-6/) (in draft, behind `level6` feature flag)
+    - [`contrast-color()`](https://drafts.csswg.org/css-color-6/#colorcontrast) function
   * [Color Level 5](https://drafts.csswg.org/css-color-5/)
-    - `color-mix()` function
+    - [`color-mix()`](https://drafts.csswg.org/css-color-5/#color-mix) function
+    - [`contrast-color()`](https://drafts.csswg.org/css-color-5/#contrast-color) function
     - Relative color syntax, e.g. `lab(from purple calc(l * .8) a b)`
   - [Color Level 4](https://drafts.csswg.org/css-color-4/)
     - `lab()`, `lch()`, `oklab()`, and `oklch()` colors
diff --git a/src/lib.rs b/src/lib.rs
index 77d904d2..297d3e8c 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -17409,6 +17409,126 @@ mod tests {
     );
   }
 
+  #[test]
+  fn contrast_color_level5() {
+    fn test(input: &str, output: &str) {
+      let output = CssColor::parse_string(output)
+        .unwrap()
+        .to_css_string(PrinterOptions {
+          minify: true,
+          ..PrinterOptions::default()
+        })
+        .unwrap();
+      minify_test(
+        &format!(".foo {{ color: {} }}", input),
+        &format!(".foo{{color:{}}}", output),
+      );
+    }
+
+    test("contrast-color(#000)", "#fff");
+    test("contrast-color(#333)", "#fff");
+    test("contrast-color(#ccc)", "#000");
+    test("contrast-color(#fff)", "#000");
+
+    test("contrast-color(#000 max)", "#fff");
+    test("contrast-color(#333 max)", "#fff");
+    test("contrast-color(#ccc max)", "#000");
+    test("contrast-color(#fff max)", "#000");
+
+    test("contrast-color(#00364a)", "#fff");
+    test("contrast-color(#00c7fc)", "#000");
+    test("contrast-color(#263e0f)", "#fff");
+    test("contrast-color(#371a94)", "#fff");
+    test("contrast-color(#9aa60e)", "#000");
+    test("contrast-color(#c3d117)", "#000");
+    test("contrast-color(#ffb43f)", "#000");
+    test("contrast-color(#ffe4a8)", "#000");
+
+    test("contrast-color(#00364a max)", "#fff");
+    test("contrast-color(#00c7fc max)", "#000");
+    test("contrast-color(#263e0f max)", "#fff");
+    test("contrast-color(#371a94 max)", "#fff");
+    test("contrast-color(#9aa60e max)", "#000");
+    test("contrast-color(#c3d117 max)", "#000");
+    test("contrast-color(#ffb43f max)", "#000");
+    test("contrast-color(#ffe4a8 max)", "#000");
+  }
+
+  #[test]
+  #[cfg(feature = "level6")]
+  fn contrast_color_level6() {
+    fn test(input: &str, output: &str) {
+      let output = CssColor::parse_string(output)
+        .unwrap()
+        .to_css_string(PrinterOptions {
+          minify: true,
+          ..PrinterOptions::default()
+        })
+        .unwrap();
+      minify_test(
+        &format!(".foo {{ color: {} }}", input),
+        &format!(".foo{{color:{}}}", output),
+      );
+    }
+
+    test("contrast-color(#00364a tbd-bg wcag2, #b10, #7b4, #05d)", "#7b4");
+    test("contrast-color(#00c7fc tbd-bg wcag2, #b10, #7b4, #05d)", "#b10");
+    test("contrast-color(#263e0f tbd-bg wcag2, #b10, #7b4, #05d)", "#7b4");
+    test("contrast-color(#371a94 tbd-bg wcag2, #b10, #7b4, #05d)", "#7b4");
+    test("contrast-color(#9aa60e tbd-bg wcag2, #b10, #7b4, #05d)", "#b10");
+    test("contrast-color(#c3d117 tbd-bg wcag2, #b10, #7b4, #05d)", "#b10");
+    test("contrast-color(#ffb43f tbd-bg wcag2, #b10, #7b4, #05d)", "#b10");
+    test("contrast-color(#ffe4a8 tbd-bg wcag2, #b10, #7b4, #05d)", "#b10");
+
+    test("contrast-color(#000 tbd-bg wcag2, #111, #eee)", "#eee");
+    test("contrast-color(#666 tbd-bg wcag2, #111, #eee)", "#eee");
+    test("contrast-color(#ccc tbd-bg wcag2, #111, #eee)", "#111");
+    test("contrast-color(#fff tbd-bg wcag2, #111, #eee)", "#111");
+
+    test("contrast-color(#000 tbd-fg wcag2, #111, #eee)", "#eee");
+    test("contrast-color(#666 tbd-fg wcag2, #111, #eee)", "#eee");
+    test("contrast-color(#ccc tbd-fg wcag2, #111, #eee)", "#111");
+    test("contrast-color(#fff tbd-fg wcag2, #111, #eee)", "#111");
+
+    test("contrast-color(#000 tbd-bg wcag2, #111, #eee, #ddd)", "#eee");
+    test("contrast-color(#666 tbd-bg wcag2, #111, #eee, #ddd)", "#eee");
+    test("contrast-color(#ccc tbd-bg wcag2, #111, #eee, #ddd)", "#111");
+    test("contrast-color(#fff tbd-bg wcag2, #111, #eee, #ddd)", "#111");
+
+    test("contrast-color(#000 tbd-bg wcag2, #111, #eee, #ddd, #ccc)", "#eee");
+    test("contrast-color(#666 tbd-bg wcag2, #111, #eee, #ddd, #ccc)", "#eee");
+    test("contrast-color(#ccc tbd-bg wcag2, #111, #eee, #ddd, #ccc)", "#111");
+    test("contrast-color(#fff tbd-bg wcag2, #111, #eee, #ddd, #ccc)", "#111");
+
+    test("contrast-color(lab(from green l a b))", "#fff");
+    test("contrast-color(lab(from green l a b) tbd-bg wcag2, #111, #eee)", "#eee");
+
+    // https://drafts.csswg.org/css-color-6/#example-62c2d8fa
+    test(
+      "contrast-color(wheat tbd-bg wcag2, tan, sienna, #b22222, #d2691e)",
+      "#b22222",
+    );
+
+    // https://drafts.csswg.org/css-color-6/#example-3a7863eb
+    test(
+      "contrast-color(hsl(200 50% 80%) tbd-fg wcag2, hsl(200 83% 23%), purple, hsl(300 100% 25%))",
+      "purple",
+    );
+
+    // Leaves variables as-is
+    fn test_leaves_as_is(input: &str) {
+      minify_test(
+        &format!(".foo {{ color: {} }}", input),
+        &format!(".foo{{color:{}}}", input),
+      );
+    }
+
+    test_leaves_as_is("contrast-color(var(--test))");
+    test_leaves_as_is("contrast-color(currentColor)");
+    test_leaves_as_is("contrast-color(#000 tbd-bg wcag2,var(--test))");
+    test_leaves_as_is("contrast-color(#000 tbd-bg wcag2,currentColor)");
+  }
+
   #[test]
   fn test_relative_color() {
     fn test(input: &str, output: &str) {
diff --git a/src/values/color.rs b/src/values/color.rs
index 274c3f43..b96d3a6f 100644
--- a/src/values/color.rs
+++ b/src/values/color.rs
@@ -1038,6 +1038,9 @@ fn parse_color_function<'i, 't>(
     "rgb" | "rgba" => {
        parse_rgb(input, &mut parser)
     },
+    "contrast-color" => {
+      input.parse_nested_block(parse_contrast_color)
+    },
     "color-mix" => {
       input.parse_nested_block(parse_color_mix)
     },
@@ -1630,6 +1633,21 @@ impl RGBA {
   pub fn alpha_f32(&self) -> f32 {
     self.alpha as f32 / 255.0
   }
+
+  /// Returns the [relative luminance](https://www.w3.org/TR/WCAG21/#dfn-relative-luminance) of the color.
+  fn relative_luminance(&self) -> f32 {
+    fn channel_luminance(channel: f32) -> f32 {
+      if channel <= 0.04045 {
+        channel / 12.92
+      } else {
+        ((channel + 0.055) / 1.055).powf(2.4)
+      }
+    }
+
+    0.2126 * channel_luminance(self.red_f32())
+      + 0.7152 * channel_luminance(self.green_f32())
+      + 0.0722 * channel_luminance(self.blue_f32())
+  }
 }
 
 fn clamp_unit_f32(val: f32) -> u8 {
@@ -3134,6 +3152,105 @@ where
   current.into()
 }
 
+fn calculate_contrast_color(base_luminance: f32, mut candidates: Vec<CssColor>) -> CssColor {
+  if candidates.is_empty() {
+    candidates.push(CssColor::RGBA(RGBA::new(0, 0, 0, 1.0)));
+    candidates.push(CssColor::RGBA(RGBA::new(255, 255, 255, 1.0)));
+  }
+
+  fn wcag2_contrast_ratio(l1: f32, l2: f32) -> f32 {
+    // https://www.w3.org/TR/WCAG21/#dfn-contrast-ratio
+    let l1 = l1 + 0.05;
+    let l2 = l2 + 0.05;
+
+    if l1 > l2 {
+      l1 / l2
+    } else {
+      l2 / l1
+    }
+  }
+
+  let mut best_contrast = 0.0;
+  let mut best_contrast_index = 0;
+
+  for (i, candidate) in candidates.iter().enumerate() {
+    let candidate_luminance = candidate.relative_luminance().unwrap();
+    let contrast = wcag2_contrast_ratio(base_luminance, candidate_luminance);
+
+    if contrast > best_contrast {
+      best_contrast = contrast;
+      best_contrast_index = i;
+    }
+  }
+
+  candidates[best_contrast_index].clone()
+}
+
+fn parse_contrast_color<'i, 't>(input: &mut Parser<'i, 't>) -> Result<CssColor, ParseError<'i, ParserError<'i>>> {
+  let base_color = CssColor::parse(input)?;
+
+  let base_luminance = match base_color.relative_luminance() {
+    Some(value) => value,
+    None => {
+      return Err(input.new_custom_error(ParserError::InvalidValue));
+    }
+  };
+
+  let location = input.current_source_location();
+
+  match input.expect_ident() {
+    Ok(value) => {
+      match_ignore_ascii_case! { value,
+        // https://drafts.csswg.org/css-color-5/#contrast-color
+        "max" => {
+          return Ok(calculate_contrast_color(base_luminance, Vec::new()));
+        },
+
+        // https://github.com/w3c/csswg-drafts/issues/7937
+        #[cfg(feature = "level6")]
+        "tbd-bg" | "tbd-fg" => {
+          input.expect_ident_matching("wcag2")?;
+          input.expect_comma()?;
+
+          let mut candidates = Vec::new();
+
+          loop {
+            let color = CssColor::parse(input)?;
+
+            if color.relative_luminance().is_none() {
+              break Err(input.new_custom_error(ParserError::InvalidValue));
+            }
+
+            candidates.push(color);
+
+            match input.expect_comma() {
+              Ok(()) => {}
+
+              Err(BasicParseError {
+                kind: BasicParseErrorKind::EndOfInput,
+                ..
+              }) => break Ok(calculate_contrast_color(base_luminance, candidates)),
+
+              Err(e) => break Err(e.into()),
+            }
+          }
+        },
+
+        _ => {
+          Err(location.new_unexpected_token_error(Token::Ident(value.to_owned())))
+        }
+      }
+    }
+
+    Err(BasicParseError {
+      kind: BasicParseErrorKind::EndOfInput,
+      ..
+    }) => Ok(calculate_contrast_color(base_luminance, Vec::new())),
+
+    Err(e) => Err(e.into()),
+  }
+}
+
 fn parse_color_mix<'i, 't>(input: &mut Parser<'i, 't>) -> Result<CssColor, ParseError<'i, ParserError<'i>>> {
   input.expect_ident_matching("in")?;
   let method = ColorSpaceName::parse(input)?;
@@ -3233,6 +3350,19 @@ impl CssColor {
     }
   }
 
+  /// Returns the [relative luminance](https://www.w3.org/TR/WCAG21/#dfn-relative-luminance) of the color, if it can be calculated.
+  fn relative_luminance(&self) -> Option<f32> {
+    match self {
+      CssColor::CurrentColor => None,
+      CssColor::RGBA(rgba) => Some(rgba.relative_luminance()),
+      CssColor::LAB(lab) => Some(RGBA::from(**lab).relative_luminance()),
+      CssColor::Predefined(pre) => Some(RGBA::from(**pre).relative_luminance()),
+      CssColor::Float(float) => Some(RGBA::from(**float).relative_luminance()),
+      CssColor::LightDark(..) => None,
+      CssColor::System(_) => None,
+    }
+  }
+
   /// Mixes this color with another color, including the specified amount of each.
   /// Implemented according to the [`color-mix()`](https://www.w3.org/TR/css-color-5/#color-mix) function.
   pub fn interpolate<T>(