Very nice and addictive game. I could well imagine a 2-player-simultan mode in this one, when 2 players fight for most points (most color-matches). Or even a 4-player-simultan mode, that could also be big fun. Alot would be going on then, on the screen, but it could be a great partygame. 4-player-adapters for the C64, are available in different stores in the meanwhile and also already known in the scene.
It would have to be designed in such a way then, that the human-players could not hit each other, when they touch (because who would always get the point then), but only the cpu-controlled players were the targets. But it could also be designed in such a way, that the human players can touch each other (so they don't run through each other), because then you could also try, to push the other human player away or to block him, when he tries to grab the matching cpu-controlled color.
A playmode like that, could definitely be fun, especially with four human players at the same time. :) I think, there would be enough colors left, from the 16 color palette of the C64, even for 4 human players.