Macbook air colorful pixels on screen
There are two possibilities: dirt on the screen, and actual internal dead pixels.

If it's dirt on the screen, then since it doesn't sound like you've tried this already, I suggest water. Water will not hurt your screen, as long as it does not run down into a crevice and into the electronics. Use a damp microfiber cloth if you have one; otherwise, use a damp paper towel very lightly (paper towels can be scratchy). Most crud that you can get on a screen will wipe away easily with wet wiping; you do not need to scrub hard, and you shouldn't as this could scratch the screen or damage the internals.

When I say “damp”, I mean getting the cloth wet under a faucet and then firmly wringing it out until it doesn't drip. Dry water off your hands so they don't drip either.

On the other hand, a colorful single pixel defect may well be a “dead” pixel. (Dirt on the screen typically doesn't look colorful except when it's fresh liquid droplets, which act as little lenses magnifying the pixels.) Typically, there is nothing you can do about these, but I have seen occasional reports of a dead pixel being restored by gentle rubbing. I would not recommend attempting this, myself.