grey dots on LCD screen

I have a Compaq Presario 1220 laptop running Windows ME. The past few days, I’ve noticed these little grey dots on the LCD screen. They don’t seem to be dead pixels or sub-pixels – if I have a black background, they’re not noticeable, but if the background is red, purple, blue, etc., I can see them clearly. No hardware or software changes have been made that caused this. Any ideas what the problem is and how to fix it?