Originally Posted by kovacm
I will ask again: do you have any reference/proof ?
The Atari 2600 had just four color registers: Colump0, Colump1, Columpf, and Columbk. There is a single color for player sprite zero , a single color for player sprite one, a single color for the playfield (and ball), and a single color for the background.
That's a total of four colors.
Any Atari 2600 game then that shows more than four colors on screen at once is proof. Qbert released in 1983 for the 2600 creates a six color screen. There are two colors for the sprites, and four colors for the background pyramid. Breakout released in 1978 also for the 2600 is an earlier example of changing color registers to increase the total number of on screen colors.
It's no coincidence that one of the people responsible for helping design the 2600 went on to design the Amiga. Seeing the usefulness of changing color registers mid-screen, he invented the COPPER.