I love to use the amaco velvet underglazes with a clear coat glaze over them.I will fire them after they have the underglazes on them before they add the shiny glaze so they don't mess up the underglazes. I make up a chart of color chips that have been fired so they can see what the colors look like after they have been fired because they often don't look like they do in the containers. This year I have purchased some glazes from Mayco, I think(i am home they are at school), that promise to be brilliant red. I have not tried them yet.
For my 1-4 students, I also use watercolor on white clay. I use the dip in watered down brown or black tempera also. The paint stay in the cracks and we sponge off the surface. Nice effect for some things.