Cherry barb turning black?

[freshienow]

A few days ago I noticed that the larger of my two cherry barbs is turning black. The orange coloration has darkened and the white scales are turning black. There has been no change in behavior. This do not seem to be an extreme problem but I would like to know what's going on. Any ideas?

 

[Lupin]

Pics? What are your water parameters?

 

[freshienow]

I know this is really bad news but I don't have a digital camera, I'll get my water tested this weekend.

 

[freshienow]

It has returned to normal, should the problem rise up again I'll make sure to notify you guys.