Bad PostCSS API

[ai]

PostCSS is not about writing CSS4 code. Many PostCSS users didn’t use cssnext.

This is why PostCSS plugins should not provide mixins or variables.

The correct PostCSS way is a PostCSS plugin, which will replace antiquebrass right in CSS to #cd9575. This plugin will be very easy:

var postcss = require('postcss');

module.exports = postcss.plugin('postcss-crayon', function () {
  return function(css) {
    css.eachDecl(function (decl) {
        decl.value = replaceColors(decl.value);
    });
  };
});

Check put also postcss-brand-colors.