A single-coloured shape with a bevel will require two printing ink colours: the original colour and black to create the shadow. The highlights are created by letting the white paper background show through. Hence, if your logo contains bevelled shapes in one colour plus other shapes in an unrelated colour, the minimum number of printing inks required is three.

There's probably no simple single general solution to this problem, so it would help if you could post a specific example of what you want represented in two colours.

Regards - Sean