Did any King Tigers have Oxide red primmer as camo instead of Red Brown toward the end of the war?

No

And a lot of the sub-assemblies came into the final assembly line painted Dunkelgelb by their manufacturer, except for cannon barrels these were a special heat resistant dark grey.

And Olivgrun was ordered to replace Dunkelgelb by spring 1945. Whether it was used, or not, is debatable, but Olivgrun was the dominant color on many late manufactured armor.