I did not know these existed. I want them!
I found these at Walmart last year. They were marked down to .25 cents a box. I bought 30 boxes of the purple ones and my k-3rd grade art classes drew Harold and The Purple Crayon pictures. They could draw anything they wanted but they could only use the 8 diff shades of purple in the box. One was almost black looking, another looked blueish and one even had glitter in it. We covered a huge part of the Art room wall with this. I have a picture of the project posted on our Art classroom Facebook page. https://www.facebook.com/WPMpurplecrayon
That sounds like a really fun project! I tried to look at the fb page but it wouldn't work. :( Thanks for looking though.