my Kribensis is a dull and doesnt have a colour

[kribmum]

I have 2 Kribs and 2 tiger barbs in a 25l tank. One krib is small and a dull grey/greeny colour with a spot on its tail, the other is a dark black like colour. The darker one always hides and doesn't surface often. Another thing i've noticed is he wont let any fish near him or on the ground floor, he is very territorial. (when i say he - i dont actually know the genders)
Am i doing anything wrong why are they so dull in colour? They both change colour when im feeding them but soon return to their dull colour. They don't look like they did in the pet shop.

 

[Colin_T]

pictures of the fish?
how long has the tank been set up for?
what is the ammonia, nitrite, nitrate and pH of the tank water?

 

[Essjay]

Is that a 25 litre tank, or a 25 gallon long tank?

If it's 25 litres, the tank is far too small for your fish, I'm afraid.

If you have 2 male kribs, one will see the other as invading its territory.
Tiger barbs are notoriously nippy fish which could be picking on the krib. Tiger barbs are shoaling gish, and having only 2 will increase their nippy behaviour. 6 is the recommended minimum for shoaling fish in general but with tiger barbs, you need at least 10 of them in the hope they'll keep the nipping between themselves. It doesn't always work. And this number of tiber barbs need a much bigger tank that you have.

In addition, if it's a new tank which wasn't cycled, you'll have problems with ammonia and/or nitrite in the water which is why Colin_T asked for those levels.