<!DOCTYPE html>
<style>
/* Matches monochrome displays. */
@media not all and (monochrome: 0) { #test::before { content: "PASS"; } }
/* Matches non-monochrome displays. */
@media (monochrome: 0) { #test::after { content: "PASS"; } }
</style>
<p>You should see the word PASS below.</p>
<p id="test"></p>