Skin fungus- skin colour change back?

It can? Tinea versacolor is the most common type of skin "fungus" that causes color changes. After it is treated the color usually returns to normal. There can be some permanent color change, but that is not usually the case. There are other fungal skin infections that could cause pigmentation changes, but they are not the usual ones.
See your doctor. See your doctor to get treated and see if it is the same as before.