Me too. The last office I was in was all grey and white. I would prefer lots of colours even if they are all mismatched. It's better than looking like a prison.

Instead of painting your office, you could print posters.

Assuming you can find a cheap printing place, there are tons of high resolution creative commons images on flickr and elsewhere.

My university has a super cheap copymat, it may be that a university near you has similarly cheap prices.

Have you taken a look at how much it would cost to repaint your office beige when you needed to? It could be worth it in the productivity gain department to paint your offices interesting colors and then contract out when you need the bigger space. Though don't skimp on the chairs to paint the office.