RTBS is pale

Fish use "platelets" to boost their colors, which require energy to operate. When fish are used to a certain day/night regimen, they in effect "get ready for bed" by turning off the platelets. This is what you are observing when you see the dull colors.

Yes, it sounds very normal. Sometimes RTBS get pale when they're stressed out. This is why specimens in fish stores look pale sometimes. I've actually seen mine be like half pale, half not. Kind of neat. Yours sounds like he's just doing it because it's night time though

Yeah, when I first brought my RTBS home from the store, he looked extremely grey and pink instead of black and red. At first I was disappointed, but within a day or two he quickly became much more vibrantly colored and is now the best looking fish in the tank. RTBSs are such cool fish to watch. I named mine Eureka because he looks like a vacuum cleaner when he's cruising over the leaves of my Amazon Swords, cleaning them off.

Sounds like yours is just fine. Maybe he's just afraid of the dark!