Here's a shader which does as ideasman42 suggests:
The values of the empty sockets in the multiply nodes are all 0.
This works by taking the dot product of 0,0,1 and 0,0,-1 in object space, and mixing two shaders based on the result.
In this case, parts of the surface facing in the +Z or -Z direction (in object space) will be black, while the rest of the surface will be blue.
Using a shader has the advantage of keeping the text editable as text.
