It is my experience that variegation can be affected by temperature, and/or by light intensity.

Less light ... and cooler temperatures ... may help recover your variegation.

Check out Optimara's care instructions here ...

http://www.optimara.com/africanvioletcare1.html

So you don't think it was the Optimara fert, at 14-12-14?

No ... I've never had fertilization to affect variegation.

Variegation on violets is caused by a several different occurrences at the cellular level and each produce a different type of variegation. No amount of fertilizer will affect these basic cellular occurrences.

Well, I once overdosed some variegated plants with Epsom Salts and lost all the variegation.

i've greened up pale/yellow looking plants with high N fertilizer, whether it affects variegation, the jury is out. it seems to appear more in winter, though, between heat and AC, i would call the temperature in my plant room mostly even....

I on purpose turned my white leafed violet green with a little epson salts. Now it is producing leaves that are mottled with white instead of all white which I think is more healthy.

Yes, agreed!

The most common reason for loosing variegation is not recieving enough light.slowly increase the light they get and I assure you the variegation will come back.also don't give them a high N fert again