Here is an idea that would look a lot better than the spotlight solution and will not introduce any noise onto your mains.
1) build an RGB colour controller, or several, they are cheap enough, although one has sufficient output to light hundreds of leds. The RGB controller project on the bigclive site is one of the best out there:
http://www.bigclive.com/this is a bit DIY, but you will really do that wall justice, and end up with fantastic mood lighting!
And for DIY lighting options:
2) build either the MR16 spotlight projects on the bigclive site, or buy pre- etched strip light strips from here.
http://www.nikamelectronics.co.uk/I have used the MR16 led lights in the garden to upgrade standard halogen lights and there is no comparison. The RGB controller allows me to either select one fixed colour, from a pallete of 16 million colours, or select from various colour wash and changing colour schemes. If you are carefull with the selection on red, green and blue leds you can get a light output that is similar to a standard MR16 halogen light.
I have also used the led light strips indoors, buying the pre etched strips from Nikan electronics at about £1.50 each and then sourcing the superflux leds on e-bay, if you want more information on the type of leds I used and the suppliers let me know.