Washed out colors, putting to sleep returns to normal

Hello everyone! I have a A1225 24” iMac with the 2.66 GHz and Nvidia 9400 in it. Upon boot, even with an SSD, it seems slow to boot. It’s running Leopard, and when booting the progress bar is a circle rather than a straight bar. (I haven’t used Leopard before, so that could be normal) Occasionally on startup, I’ll get one long beep before it boots up. The main issue is the screen is washed out and colors are inverted until it is put to sleep and then the colors return to normal. Is there an easy explanation for this?