; Fill half of the memory with one and other half with another colour

LDA #$09
LDX #$00

LOOP:
STA $0200, X
STA $0300, X
DEX
BNE LOOP

LDA #$03
LDX #$00

LOOP2:
STA $0400, X
STA $0500, X
DEX
BNE LOOP2