emacs 24 color-theme not working

emacs 24 color-theme not working

I'm running emacs 24 and trying to change the colour theme but it's not
working.
When I start emacs it displays in the default colours. I do M-x load-theme
RET tango RET and the colours revert to white on a black background (other
themes do the same thing).
I'm running emacs on debian wheezy through a putty window on a Windows 7
host. I've tried a local instance on debian with no change. I've tried
both a pre-built package and building directly from a git mirror.
I'm something of an emacs newbie so it's possible I'm doing something
stupid. Any help would be much appreciated.
Thanks,