Thanks to everyone who helped me decide what to do with my snowflake Zendala. I decided to go with Cat's advice and use blue. I used about 10 different colors of Prismacolors in shades of blue, white, and silver and used them as if I was shading it. I really enjoyed this process and think I will have to explore it more. Here it is in blue.
And, since I accidentally had my scanner set to black and white mode for my book; here it is in black and white. I think I achieved my goal of "shading" with blue. Except for the center, it looks just like it would have if I'd done it with pencil.