ok , my fish chnging color it's an fantail goldfish and wan buy it was rad and slvr and now he have this black stuff on hes tail i not shur wath it is ????? is it a dasis or just color cang plz plz plz i need to know caz if it is a dasis i need to go and buy a madikl soooooooooooooo come on ppl i need to know ok thanx IF SOMEONE ANSWAR :( :( :( :( :( :( :( :( :( :(

I think from what you've said, the color change was pretty quick. So, it's probably an indication of a problem. Black color can be from the area being injured. If you could post a photo, that would help diagnosis. I'm sorry for your distress and that of the fish.

One time I brought a black and orange goldfish, and months later, it was a dark orange. Was this normal?

Slow color changes are very common. Black (mostly on fin edges) is normally a transitional color for goldfish as they grow. Many of my common and comet goldfish of ordinary color started out brown/black/natural and then went to orange with black-tipped fins and then to orange/red with white tipped fins. My site has a few sections on goldfish color changes. Slow changes are normal but fast (a day or two) ones are not.