Stylelint offers the option [[ http://stylelint.io/user-guide/rules/no-indistinguishable-colors/ | no-indistinguishable-colors ]], which allows to set a threshold for separate colors being included in CSS/Less code. From a UI Standardization point that seems incredibly helpful as it should help prevent “having 5 shades of pale light blue, for example, [when] you probably wanted just one”.

A threshold of 2 seems useful.
It returns the following linting feedback (test run on current Echo codebase at threshold 2):

modules/nojs/mw.echo.special.less
121:22 ✖ Unexpected indistinguishable colors "#f6f6f6" and "#f1f1f1" no-indistinguishable-colors

modules/styles/mw.echo.ui.NotificationItemWidget.less
247:21 ✖ Unexpected indistinguishable colors "#ececec" and "#f1f1f1" no-indistinguishable-colors
253:22 ✖ Unexpected indistinguishable colors "#fafafa" and "#f1f1f1" no-indistinguishable-colors
253:22 ✖ Unexpected indistinguishable colors "#fafafa" and "#fff" no-indistinguishable-colors

With threshold 1 it just returned:

modules/styles/mw.echo.ui.NotificationItemWidget.less
253:22 ✖ Unexpected indistinguishable colors "#fafafa" and "#fff" no-indistinguishable-colors

The only caveat that I've run into, it doesn't seem to take opacity in rgba notation into full account and therefore also leads to

377:10 ✖ Unexpected indistinguishable colors "#000" and "rgba( 0, 0, 0, 0.1 )" no-indistinguishable-colors

I need to look closer how we can best-address this, but from first test runs this addition to our general stylelint configurations is a “go”!