hi, what a pretty fish, and nice color
i would have thought it was his color too,
you are speaking the "kidney bean" shaped area to the left of the gold-ish circle.
you said "been like that since we got him" ... how long have you had him?
in looking at the picture, it doesnt appear red or "angry"
after you examine him closer (remove rings, no lotions)
if it is not just his coloring:
it may be a spot that is healing.
you dont know how he was handled before you got him.
if he was netted, sometimes the slime coat or scales can be damaged.
because it doesnt look "open" bleeding,
with good water conditions, he will heal
if its just his coloring,
with good water conditions, he will thrive

If you do find "something" post back your finding, trying to include answers to the questions listed in the red box. If he does need treatment this will help other members to give more accurate diagnosis.
you have a really pretty fish,
-Tooter