The "Color>Apply Color" operation is for hardware rendering, it will show up in the viewport or if you use the hardware renderer but not with any software renderer. Go back to "Apply Color" and choose the "remove color" option this time and it should be back to normal.

Honestly, instead of trying to apply separate shaders to faces (which will result in razor sharp transitions between colors) It would be better if you used the 3D paint tool so you can paint where snow, grass, dirt is supposed to be then save that out to paint over in Photoshop, or maybe you'll get it as detailed as you want right inside Maya.

1.Assign a new shader to the model, lambert if you don't want to deal with hardware highlights.

2. Assign a file texture node to the color slot of the shader and leave the file path blank.

3. Select the model and go to the "Rendering" menu set. And under the "Texturing" menu choose the 3D paint tool>options.

4. In the option box, under "File Textures" press the "Assign/Edit Textures" button and set the resolution and file format for the texture, hit "Assign/Edit Textures".

5. Paint away and "Save Textures".