Dick Blick has some really great tempera paints that come in dried cake form, like huge watercolors, that can create a translucent effect like watercolors but also can be opaque. They are great for color mixing as well.
Last week in my first grade classes we talked about how we can apply the ideas of addition and subtraction to mixing colors. They have learned a lot about the primary colors and what colors they make, but so far it has all been theory. So the last few classes we had, we put our color theory to practice.
Needless to say, they had a ton of fun.
I made (I hate to say "worksheet" but what else can I call it?) a worksheet to guide them through the mixing process and copied it onto a heavier drawing paper that would hold the paint, and they set to work.
The finished products looked something like this: (I know, the pics aren't the greatest quality, but you get the idea, right?)