electricalgroundingjunction-boxwiring
My brother has a metal pancake box directly screwed into a 2×4. That same screw used to fasten the box is also being used to ground the box.
i.e metal pancake box screwed into the wood also has the ground wrapped around it.
I know ground screws inside the box must be green – I am more concerned over whether or not what I described above is safe.
The simple answer is get "self grounding" duplex outlets. The typical design has a little spring plate meant to connect your grounded metal box to the outlet yoke, and thus to the third prong. Just install, test the ground with an inexpensive outlet tester, and feel lucky that the builder left you in such good shape:
If you are in the United States: surprisingly these are legal even in new construction. Beyond that, they're perfect for your retrofit. See the National Electric Code (NEC) section 250.146(b). Note that your ground wires may 16 guage rather than 14 or 12. That was OK at the time, and you're not required to change it now.
The fact that it's a wet location doesn't make a difference to how you make your wire connections (although it needs to be on a GFCI circuit because it's for a pool light). Connect a pig-tail ground wire the green screw on each of the switches and a 3rd one to the green screw on the box. Wire nut all three of them together with the ground coming into the box.
Best Answer
Ground screws do not need to be green.
Though they sell some very cute green ones ten for a buck if you want them to be green.
Ground screws must be -32 thread pitch or finer, and must be threaded into the metal box. 10-32 is the "conventional" size. And most metal boxes have a hole tapped for a #10-32 screw for precisely that purpose.
This is visible as a hole slightly smaller than the normal mounting holes.
If you can't find it for love or money, likely someone has driven the physical mounting screw into that hole. Better boxes try to help deter this by putting the ground screw on a stamped "bung". That also gives the ground screw a place to go besides straight into the wall, but if someone misused the hole for a mounting screw, that problem will be solved :)