I’ve used WebAIM’s Contrast Checker forever but WhoCanUse is a new color accessibility checker that adds some nice features and is certainly better looking. The breakdowns by each vision impairment with visual examples and percentage of people affected seems especially useful.
“Living with colorblindness feels like you’re constantly being pranked by the world in subtle, irritating ways.”
From This is what it looks like to be colorblind by Andy Baio over on The Verge. An interesting look and some interactive examples visualizing the idea of colorblindness.