lemon tetras turning black?

[cudamaster13]

for somereason my three lemon tetras are turning kind of a dark and black.wat does this mean and how do i fix this?

 

[Redearsunfish]

no idea. maybe they are males?

 

[Allan01230]

Do a 50% water change if it is an established tank. IF it is a few months or so old just do a 25% water change. Keep us posted.