This is great. It's easy to skip over this and its difficult to accurately foresee (no pun intended) issues for those with colorblindness without a tool like this.
This would be a nice addition to @marwannas's Helping Hands collection.
A great eye-opener in terms of accessibility issues for web designers. Some types of color blindness affect approximately 1 in 12 men and 1 in 200 women in the world.
There's a nice introduction to the extension over here.
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