I do primary, secondary, comp., and mixing separately, revisiting them
frequently throughout the grades.
Why not have your 8th graders design a mandala using the color wheel?
You can have them look at the web site
http://www.zayantecreek.biz/tiledreams.htm and
http://www.mandalaproject.org/Index.html to see a wide variety of
mandalas, some with the color spectrum incorportated. Notice on the
zayantecreek site that you can order a beta version of tiledreams for
your exploration.