Question
Two of my A V; bi-color red and white have changed colors to nearly all white.  Both plants are healthy which had about the same percentage of white and red in their blooms; heavy with blooms until this fall, when I cut off the last of the spent flowers.  Serval weeks ago when they started blooming again the color had changed to an all white flower with a few of the blooms having a little of the red color.  One is an Optimara and the other I don't know.  Both bought at local nursery in 2006.  Both are on window sills, one on the East side the other on the West.  I fertilize with ever watering  watering from the bottom when the plant feels light when  picked up.   I live in Bakersfield, California; at night the furnace is turn off and during the day temp is kept at 70.  At night it does get cold but my violets don't seem to mind.  Night time temperature in the house I'm not sure of.
Is this color change caused by the colder weather and less sun light?  Will they bloom back again to their 50 percent red and white this summer?
Thank you for time.   Oh yes, they are still very nice plants.
joe

Answer
Joe,
Let me apologize first of all for the delay in answering your question.  

I applaud you on your care and knowledge of your AVs.  You seem to really know what they need, and you must be experienced in either African violets or gardening of some type!

Your question required me to do a little research.  What I found out is that variegated violets, such as your's, can lose their colorful markings when they are too warm, such as in summer or when their surroundings are too warm.  That does not seem to be the case with you and the temperatures you mentioned.  Another thing that affects markings is the acidity or alkalinity of the soil.  Since your violets' markings are in the PINK/RED family you would want your soil mixture to be slightly alkaline.

Lastly, let me mention repotting. A woman who judges African Violet shows believes one should repot established violets at least twice a year.  She says this prevents nutrient depletion, since most AV mixtures contain perlite or vermiculite, and very little actual soil.  If you are not employing this technique you might give it a try.  This makes sense to me, and I think I will try it myself.  

This is about all the info I could locate on the subject of variegated violets and the problems you  are experiencing.  I hope this has helped a little.  Good luck.