I don't know that "all" models had painted carbs starting in 72, but some seem to have.  I worked on a DT2 a couple years ago that had what looked to be a factory painted carb...  but I'm not sure I checked the stamping, could have been someone bought a new replacement at some point and it came painted because DT3 was painted and they take the same carb?

I think I remember one CT3 carb painted but not sure if that was original.  I have a few 72-73 AT/CT carb bodies and none look like they had paint but it could have been cleaned off. None have caps which a lot of times people didn't take off cable to clean so sometimes stay painted.

By 1974, it seemed like most were painted?

Assuming that mine havent been painted my LT2 is black, my 74 DT250 is not painted but has a black cap, my 75 DT250 is black, 73 RT360 is black.

Perhaps the gal/guy painting the carb's couldn't keep up?
Sneezles61