Black Guppy Changing Colour?

[friendsnotfood]

Hi

I have a black (extremely black) guppy, i've had him for about a month now. He is quite small (compared to others in fish store) so guessing fairly young?
About a week ago i noticed that a part of his tail was starting to look lighter, a yellow colour, then he went completely black again. Then i keep noticing occaisionally that his body will look more of a metallic blue and then go back to being black again.
I have tried to look for a pattern (if it happens a certain time after having lights on etc) but cant notice one.
My tank has been cycled for a couple of months now and consistantly tests at ammonia 0, nitrite 0 and nitrate 20.

Is my little guppy ok?

Thanks

 

[PrairieSunflower]

Do you have female guppies in your tank as well? Male guppy colors can change somewhat when they are "excited" about females and showing off. For example with my lighter colored ones, their colors get darker. I used to have a delta with a black tail who took on a blue sheen.

Does that sound like what could be happening to your guppy?

Also, if it was small when you got him, he could take up to about age 6-8 months to develop his full colors.

 

[friendsnotfood]

Thanks for the reply

No, i only have a couple of males.