one of my firemouth has very dark black stripes down his sides, while my other has very slight black stripes. however when i look at them on the net in photos none seem to have these stripes. Is this because they are still quite young.

Id say its probably because of stress but wtihout pics, tank setups etc we cant realy know for sure....

What size tank are they in and what tankmates do they have? they seem to be getting bullied at all?

i have try geting photos but camera not very good, but i think stress is probaly the answer because it is the smallest firemouth what gets the black stripes, i keep both of them in a heavily planted tank but have noticed the bigger one annoying the smallest. there is only 2 firemouths in the tank and two cories. theyare being moved into a bigger tank as soon as it has cycle new tank will be 215liters current tank is only a 100liters.

When they 'colour up' or are sleeping the stripes show. At night they go pale white, but the stripes go dark, when they colour up they go a dark grey with black stripes.

When stressed I've found Firemouths go pale, not dark.

Mine 'colour up' e.g. go darker when they've found a rock to guard, or are at least in breeding condition. Unsettled or frightened they are pale.

The stripes are much less noticable on the larger adult Firemouths. Younger Firemouths also tend to have blue eyes which looks sweet.

both my firemouths still have a blue look to their eyes, when i bought them they had no colour at all i thought that was because they were young. they were crowd in a tank with no cover thought bar small piece of driftwood. They seem to have divided the tank in half the smallest stays pretty much down one end. The bigger one swims around a bit more but has a corner where he sleeps. The smallest sleeps in the other corner behind a rock