I think you should re-read the question, because "frequency of the metal" doesn't make much sense in this context. And the color of photon is dependant only on it's frequency which is given. Do you need some further explanations on that?
Photoeffect's main equation is one of energy balance. The only energy source in this event is the photon whose energy is $hf$. If that is enough to eject an electron ($\ge w$), the emission occurs. The leftover energy becomes kinetic energy of the electron.
The threshold is the case where you get just enough energy to emit the electron but no leftover. The needed equation is $$hf=w$$