Preserved Topic: Transparency On 2 Different Colors

Hello everyone! I searched for help on this specific topic but could not find any answers so maybe someone can help me out. I?m trying to design a sig with a transparent background to use on a forum. I understand the idea of selecting the correct matte color however, what if the background changes from two different colors after each post. For instance when you post on the message board I am referring to the background is F1F1F1. Then, when you post again the background alternates to DFDFDF. Each post alternates between these two colors and I was wondering what the matte color should be set to in order for the transparency to look right on both background colors. Make any sense? Thanks for any help guys!

#e8e8e8 is the matte, the average of the 2 colors. See tutorial: http://www.gurusnetwork.com/tutorial/gif_transparency/ specifically, this page: http://www.gurusnetwork.com/tutorial/gif_transparency/3/