Can my guppies be turning yellow?

[flavia21]

Hey everyone!
I just noticed a change in color with some of my guppies.... Especially my female(oldest) who just used to be white and black tail.
Anyone know why? Can it be something with the water?
Would appreciate all advice!

 

[flavia21]

Anyone?

 

[Stellah]

I'm pretty sure your fine. They can develop differently based on diet changes, and age. Even temperament and stress. She looks good to me.