I agree with Dorothy, sounds like a bit of a messy project on a piece so large.
The main reason that people choose white is so the colors of the work is not affected. I actually have one white one, one black one.
If you do want to have a design wall in color, rather than a dying project have you considered buying 72" wide felt? It comes in many colors. I feel felt makes a nicer surface than flannel for this purpose. Just a thought.
Here's an example:
http://fabricdepot.com/index.php?pag...rchstring=felt