It was not an option in 1979 however it was in 1976 on the Spirit of 76 trucks.
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It was available in '79 and '80 as a two tone interior. Pickups, Burbs and Blazers. You could get red/white, blue/white, and gray/white (that one might be '80 model pickups only). Possibly green/white too, I don't really remember for sure.
The seats, door panels and console if equipped were white, everything else was the secondary color. I don't remember about the seatbelts either, I'd have to look through all my old saved pics.
The headliner trim was white too, of course. Just like all of them in those years.