Accessibility Color Wheel
This is an invaluable tool for picking colors. It’s very cool too.
Use: Choose a foreground color by pointing the mouse over the wheel or the grey stripe and click. Then click the “Background” button and choose a background color the same way. If OK becomes visible down here the color pair is good for accessibility. Otherwise change one color or both selecting foreground and background by left buttons. Ok in the single textboxes means the contrast/difference in brightness is good.