Just to correct the record, when I first saw these jerseys 2 years ago:
I could only find them in that photoshoot and only found the shorts here in some actual game footage/documentation:
So I assumed they were just used for promotions or for a preseason/exhibition game. But then after digging a bit more when the Rockets announced the new classic, I found this program as well:
So the best I could figure out was that it was just a variation of the home jersey that they wore during the 1967/68 season. The rockets had a few of those variation jerseys during the 60's which were like alternate versions of their home and road jerseys. Not a lot of quality control and consistency during those times.
(Also, sorry to cross promote but the correction is up on my website too if you guys are interested)
