
Hi, I have these fish, and can only say they get VERY dark "Brick" red....not a bright scarlet, or blood red. They are nice in a tank, I tried taking a picture of mine just now, but the color with the light from windows behind, just didn't do it justice, so I didn't down load it....I'll try to get a night time and post it later.
You can already see the contrast of silver, that continues to show. With a male and female you will have the most vivid colors.
I have to say here though that these fish do get up to 4-6", mine is about 5", and along with the other fish you currently have (balas especially), you need a much larger tank.
The balas need 72" length in their tank, they are fast and active fish. The other problem at this point is that 40 on nitrates is double the "safe" limit and you need to up your water changes. This is one of the down sides to overstocking a tank, and will lead to disease because the fish are stressed. Good Luck, It sounds like you have interesting taste in fish....