The RPs were in Dark Green, with a coloured band denoting the warhead type. There is a drawing of this in a thread in the modelling section, covering a Beaufighter in the PTO, which shows the colours and markings.
The colour of the rails would depend on the type, early or late, but were mainly in bare metal, although not shiny like, for example a NMF Mustang ! In some photos, they appear to be Medium Sea Grey, but this seems to have been rare, and is more likely to be dull metal.
Note, if this is for a model, you will need to check the squadron concerned, as the RPs and bombs were NOT interchangeable; there were separate squadrons assigned to RP use and bomb carrying.