Its up to you to keep it or not if its doing ok in freshwater, though you might find the reason it hasnt coloured up is through a lack of salt.
Its shops ordering them in off the fishlists, they are just lumped in with all the other cichlids and if you didnt know it was brackish, you wouldnt find out until you got it and generally, they do ok in freshwater especially for short term in the shops. Kind of like Figure 8 puffers (only these fish genuinely do come from tidal brackish areas).
It might be that they were caught quite far up the estury and was considerably less salt but i doubt it, suppliers would catch them where there is a good number of them.
Unless you can find a brackish home for him.... or better still, set up another tank

they are a shoaling species of cichlid and you could find a few more
The orange chromide is Etroplus Maculatus, i know there is a green chromide as well, not sure if its a colour variation or sub species.
There is also a freshwater cichlid called Pearly spot cichlid or Etroplus canarensis which is what I had a shoal of a while back

shoaling cichlids are awesome!