How to go about Tile grid in 3d game? +How to make textures transparent?

Hi. I'm currently working on a turn-based game that works with tiles mechanics. Check this video for example: http://www.youtube.com/watch?v=l39sKjCGxyM (4:40).

However, my game does not have set camera, instead it follows each character from third person view. That's why I'm currently generating flat cubes and putting desired texture on them. Is that the best way to do it?

Another question is about transparent textures. Basically I'd like to get the green overlay like the video shows it. How should I do it? Do I need to apply certain shader on the material? It would be the best if I could import white texture and then somehow set the color in code. How can I do it?

Thanks in advance.