changing default post icon by forum?

[khininger]

Hi,

I have post icons that users can choose for their post when they make it, in any forum; for example, green, yellow, and red. Default is "no icon". I want to change this default selection for some forums, i.e. if they are making a post in the "green" forum, their default post icon selection should be "green", not "no icon". They should still be able to select "yellow" or "red" though.

Is this doable? Which templates should I look at?
Thank you very much!