I am twiddling my thumbs a bit whilst I save up for my scanner parts, but I thought this was a fun way to get to understand colour.

http://color.method.ac/
check it out, it also has support for tablets, and even adjusts for colour-blindness.
You go through colour matching for hue, saturation, complementary, analogous, triadic, tetradic etc. and it is a lot of fun and an interesting exercise.

The best way to play this is to look at the colour swatch and then click precisely where you think the required colour would be.
You can then see how far off your initial impression was, and then slide about until you get the colour to match the requirement.
If you just start sliding from the get-go, you might get a better score, but I think it is more interesting to know how far off your first estimate was.

The colour controls are quite similar to those in most colour grading packages, so it is a fun way to get the hang of how those controls work, and improve your understanding of colour.

Post your scores!