Blender supports 16 materials per mesh. So with that in mind, you can use 16 different colors/textures on a single mesh. After that you have to get creative and break the mesh apart if you need more colors as in the case of architectural models and so forth…
Easy is a relative term, but I would say yes, it is easy.
Let’s assume you are working with the default cube.
Select the cube.
Put the cube in edit mode. (TAB-Key)
Chose face selection mode.(CTRL-TAB 3)
Select a face. (Right-Click on face)
Press F9 Key to activate the editing context.
In the Links and Materials Tab Click the New button to add a new material to your cube. Then click the Assign button to assign the selected face (or faces) to use the new material.
That is all there is to it.
Be default, the New button will clone the current color, so in this case, your cube is still all the same color, but the selected face is linked to material #2. All you have to do at this point is click on the Color swatch and chose another color and your selected face will change to that color.