Does tamiya ever discontinue paint colours?

Yes, the downside to Tamiya colors is that before the new releases their colors were all generic and not matched to any standards such as ANA, FS, BSC, RAL, or RLM. They were all just “kinda sorta” on their camo colors. Most of their new colors are supposed to be matched to something now, NATO, JGSDF, IJN, RN, RAF...

A number of years back their spray can primers were not available for reasons of content and the way it was listed, but that was fixed. For that reson I stocked up on a dozen cans each of gray and white. Down to a couple each now.

As far as colors, I like their paint when I'm freelancing a match, say wood for a deck or red hull bottoms. But I find it really hard to get matches to actual colors such as Ocean Gray, Haze Gray or any of the German aircraft colors.

So far, no they have not. And in the past 10 years or so they have expanded the line a bit with some new color additions every so often.