On the C64, when scrolling, the fastest way to update the screen colour RAM (which cannot be pointed to another address, unlike the screen character map) is to

On the C64, when scrolling, the fastest way to update the screen colour RAM (which cannot be pointed to another address, unlike the screen character map) is to do it all with immediate LDA #$xx / STA $D800 / LDA #$xx / STA $D801 / etc (where xx are your colours, and $D800 is the base address of the colour RAM) - then during the 7 frames of pixel scrolling, you both offset-copy the screen characters to the second screen buffer, and also move all the character colour info (the values throughout the previous LDAs) through the colour RAM update code, and on the 8th frame you flip character screens and then call the colour RAM splat subroutine. [edit] It's much faster than the obvious solution, which is to do LDA $D801 / STA $D800 / LDA $D802 / STA $D801 / etc. Or, even worse, a loop incrementing the X register with LDA $D801,X / STA $D800,X / etc. Or worse still: indirection via zero-page (though no-one should really ever consider that for colour RAM updates, even though at first glance it seems clever for moving the characters between screens, it eats too much time) (This technique is pretty much only applicable if your scroll is fixed-direction and fixed-speed) [edit #2] Credit for that goes to Jon Williams (Shadow Dancer, C64 - and others) for adding that optimisation to my scroll routines that he used in SD - and for then telling me the trick :)