How do I fix my zsh prompt now that I've upgraded to snow leopard?

I recently upgraded my system to snow leopard and now my prompt doesn't work properly. I have this line in my .zshrc file:

PROMPT='%{$fg_no_bold[cyan]%}%n@%{$fg_no_bold[red]%}%m%{$fg_no_bold[green]%}$(git_branch)%{$reset_color%}: '

(where "git_branch" is a function that give me information about the current git branch I'm working on). The problem is that the colors and "git_branch" function aren't being evaluated, they are taken literally, so my prompt is:

%{$fg_no_bold[cyan]%}username@%{$fg_no_bold[red]%}machinename%{$fg_no_bold[green]%}$(git_branch)%{$reset_color%}: 

The colors are nice, but the part I'd really like to get working is the git branch info. I've been googling, but haven't found anything yet. I'm a bit of a noob when it comes to zsh, so links to helpful resources would also be apprecia开发者_StackOverflowted.

zsh --version
zsh 4.3.9 (i386-apple-darwin10.0)

After looking at a bunch of config files I discovered that adding these lines:

setopt prompt_subst
autoload colors

colors

caused my prompt to correctly interpret my color codes again.