My .02 cents. You can use any colour wire you like on switches, the trick is to Mark your switched wires so you know what they are. This is easily done with coloured tape or even with masking tape and a pen. That said getting new wires through old conduit is either a pain in the neck or impossible.
You probably already know this but: Red, black and blue wires are the colours for three phase wiring. Most houses only have so called single phase wiring. This is confusing terminology because that means a house has two phases coming in Not one as the name seems to indicate. I can kind of see why an electrician might use a handy spare four wire conduit for 3 way switches. After all it is just a wire...