Thank you very much for the tip. I am indeed using separate brushes. I use 1 for color #8, one for browns and one for lighter colors. However, I do think it is an interesting topic to if polish residue will transfer on brushes. My understanding is that the primary purpose of the brush is to remove any excess residue, dirt, etc so why then would it add residue back to a finish?
It has been my experence however that ravello and whisky naturally darken with age .This could well be what you are seeing. I am of the school of thought that given time and exposure all shell will eventually reach pretty much the same shade of medium brown as long as tints are not introduced
sorry double post