In the electro-mechanical version, the walls are a series of panels that have a capillary system built in. You can change colour at the touch of a button. When you do, a different colour dye is pumped into the capillaries, and almost instantly you can change the mood and colour of the room.
In the electronic version, the walls can display any blank colour, or they can display your photos or murals. You can have custom graphics done in programs like photoshop for specific occasions (Happy Birthday comes to mind).
Rooms can be jungle rooms, or seaside rooms, or peaceful blue or disco orange. You can change the room depending on mood and circumstance. If you are having a big party, you could even make a few bucks by selling the advertising space on your walls.
This change in wall material will change the world of graffiti as well. Someone will come up with an iPhone to text graffiti onto the walls in public washrooms. This will add a whole new dimension to bathroom-wall limericks. I am still trying to think of a rhyme with:
Here I sit and try to text .... ..... ..