Disease Sick Or Normal?

Just got two new oscars a I noticed they r starting to turn yellow after two weeks and I noticed this after a 50 percent water change and a Chang in conditioner all tho my tap water only has .25 chlorine level without any conditioner. ammona level is zero so I don't kno is this normal? Could this be there colors and becuz the new tank they where hiding there colors??? Plz help me they r eating and don't seem stressed

this is very normal oscar behaviour,
they can change colour in the blink of an eye.

so long as your water conditions are ok there is no problem