It sounds like you are describing bottled rainbows. Charismah did a gorgeous one pictured here:
http://www.quiltingboard.com/picture...2-t118490.html
A link to the tutorial is right in Charismah's post but here it is as well:
http://www.stitchedincolor.com/2011/...ape-quilt.html
Edited to add, if you don't feel like following the whole blog here is a link to the nitty gritty of construction
http://www.stitchedincolor.com/2011/...w-to-make.html