Sounds like the pink wire is for the clock and radio station pre-sets (it'll need constant power so you don't have to re-set the clock every time you start the car). You can find a fuse that is "on" all the time and hook to that or directly to the battery.

Red is probably main power that it only needs when the key is "on"

The screw is for a strap of metal you can attach to the firewall so the back end of the radio doesn't flop around.
Best,
Shayne.