Change colors to be more readable in light themes (#10890)

Some of the text colors used by dune tend not to be readable on
default light-themes terminals. Of course it will always be possible
to configure your terminal so that some colors are too light/dark to
read, but some of the preset themes on macos are unable to display
some colors commonly used by dune.

Signed-off-by: Stephen Sherratt <[email protected]>

Author: gridbugs

doc/changes/10890.md

@@ -0,0 +1,2 @@
+- Change some colors to improve readability in light-mode terminals
+  (#10890, @gridbugs)

otherlibs/stdune/src/user_message.ml

@@ -159,9 +159,9 @@ module Print_config = struct
     | Kwd -> [ `Bold; `Fg_blue ]
     | Id -> [ `Bold; `Fg_yellow ]
     | Prompt -> [ `Bold; `Fg_green ]
-    | Hint -> [ `Italic; `Fg_white ]
-    | Details -> [ `Dim; `Fg_white ]
-    | Ok -> [ `Dim; `Fg_green ]
+    | Hint -> [ `Italic ]
+    | Details -> [ `Dim ]
+    | Ok -> [ `Fg_green ]
     | Debug -> [ `Underline; `Fg_bright_cyan ]
     | Success -> [ `Bold; `Fg_green ]
     | Ansi_styles l -> l