ld hl, $C000       ; CRAM address $0000 with top two bits set to indicate a CRAM write
    ld c, $BF          ; writing to control port
    out (c), l         ; output address 
    out (c), h         ; 

    ld a, $FF          ; lower byte of color data
    out ($BE), a       ; data port write, CRAM unchanged, latch = $FF


    ld hl, $C021       ; CRAM address $0021 with top two bits set to indicate a CRAM write
    ld c, $BF          ; writing to control port
    out (c), l         ; output address 
    out (c), h         ; 

    ld a, $0F          ; upper byte of color data
    out ($BE), a       ; CRAM word at $0020 is now $0FFF, and the data at $0000 is unchanged.