UI Update : Using a more noticeable image

[xirclebox]

First off, great job on this project. I just learned about it today and I've added it to my design toolbox and shared it with the rest of my team. One thing that I noticed is the use of the very light image for the "Don't use" values. Even though I don't have a problem with contrast, it's possible that you'll have someone who does who would like to use your tool. I would suggest using an image that is more noticeable to convey those color combos that aren't compliant.

Keeping with the clean approach to your design, please consider my proposed update to the UI.

Thanks and have a good one.