The memory address 53281 ($D021) is used for the background color of characters and graphics (HiRes) of the C64 and is set in BASIC with
POKE 53281,X, where X is a number from 0 to 15, giving a total of 16 colors.
The standard colors of the C64 are:
10 X = X +1: IF X>15 THEN X=0 20 POKE 53281,X: POKE 646,X 30 PRINT " * C64-WIKI DEMO "; 40 FOR Z=0 TO 150: NEXT Z: GOTO 10
This C64-Wiki demo program prints screen text in all of the different colors available and cycles through the background colors - break by pushing the RUN/STOP key.