Sorry I haven't been keeping up with the challenges, but I thought I would offer one for this short week.
I would like to see what you can do using black paper. It can be really striking. Try some of your color mediums to see what shows up well and what doesn't. I know I have interference colors in a few different mediums, they look best on black or dark colors. As an alternative, don't add color at all, just use a significant amount of black paper on your project.
If you don't have black paper or card stock, you can use black paint or ink to make some, or use another very dark color like navy, but I'd prefer black if possible.
Good black card stock can be hard to find. Some are blacker than others! Let us know in the discussion if you have a favorite black card stock.
I hope you get a chance to play.
I have an idea in mind ... hope I can get it on paper!