Dyed Cigar, how to tell?

[JJG]

On some of the darker cigars I've smoked, I noticed that a strange lighter colored ring appears next to the ash. I always assumed this was a telltale sign of dye. just a guess though, I could be wrong. It only happens on really dark smokes though.

anyone else know what I'm talking about? It's like the wrapper turns a different color as it starts to burn.