Subject: What is responsible at the cellular level for red and white colors of yeast

I am doing lab work currently on yeast and I am a little confused as to why 
some yeast I grew on a media plate has a patch of red in the middle with a 
white border and everywhere else on the plate there is white yeast.  I know 
that both the red and white are one strain and the same sex.  The genotype of 
the yeast strain I am working with is alpha ade2 ade3 ura3 leu2 trp1 
lys1/pDK255 LEU2 ADE3.  So knowing all these things I'm hoping will help.

Re: What is responsible at the cellular level for red and white colors of yeast