Hi Ken,
I think that replacing the "paint()" command with LINE (0, 0)-(800, 325), _RGB32(116, 205, 255), BF may be a little more efficient...
Principle: (correct me if I am wrong) A floodfill needs to process surrounding pixels from the 'start point' and either continues check and plotting, as it goes, until it reaches a predetermined colour or the edge of the screen. Doing this 30 times per second could cause a lot of memory usage and on some older machines it may impact performance... There is probably a lot more involved but this is 'my' understanding... lol