Bronze Cory, red-ish belly, normal?

[Ruby011]

Hi, so I'm pretty new to keeping fish. I've had my Bronze Cody cats for about 2 months now. (3) and I have 2 panda cory cats in the same tank (6 months) with a stray albino cory cat.

I noticed that the Bronze corys have pinkish, redish bellies, whereas the others don't.

Is it normal for them, or is there something wrong?

 

[QualityAquatics21]

A picture would be nice.

 

[Colin_T]

How long has the tank been set up for?
What is the ammonia, nitrite, nitrate and pH of the tank water (in numbers)?
How often do you do water changes and how much water do you change?
Do you gravel clean the substrate when you do a water change?