Light switch with same color wires
Sounds like you need a neutral wire for that timer switch to work. It's simple logic really: the timer has to get power to run the timing mechanism whether the lamp is on or off.  There are clever ways to steal power when the lamp is off, but not when it's on.  So it needs a hot (which will be one of those wires) and a neutral.  

Both wires being the same color is a hopeful surprise.  Same-color NM is hard to find, so good chance your wires are single-wire THHN/THWN in conduit, and the electrician ran two blacks (or whichever color he used) because it is a correct color for both always-hot and switched-hot.  You may be able to pull a neutral wire (white) by fishing.