http://www.alsacorp.com/products/retroglow.../retro_show.htm
Apparently the glow stuff goes on invisible... if you were to do glow flames on a colored background, they wouldn't show at all unless it were dark.
Taking this idea further, what if you did one flame pattern with colored paint, say, yellow on red, and then a different COMPLIMENTARY flame pattern that only shows when it's dark enough to be seen?
The possibilities are endless!!