Carol - it is a shock from a spray/temperature change/light change. In your case - looks like it is from your spray. Probably next bloom will be normal.

I just read on the Gesneriphiles forum that the low intensity of the light (in one of the examples the tubes burned out - and the grower didn't catch it for several days) brought the significantly lighter bloom on streptocarpus - and when the tubes were replaced - the next bloom came normal.

I.