Redmine

You can already apply custom themes to Redmine. I don't know if there are specific instructions anywhere, but it's good to start here:

http://www.redmine.org/boards/2/topics/show/100

The theme name is the name of the directory. You have to select the theme through the administration page once you've completed it. I have set up our work with a theme that adds priority colouring to issue lists. Can't remember where I found it though as it was several months ago.

I wasn't very clear..

I know that themes can be created and used, but a theme changes the look for all projects.
I was asking for customization per project: each project with it's own logo/colors.

Ok - got you now.

One solution maybe to make a small modification to the Redmine templates such that the project identifier gets inserted as a CSS class on the outer most DIV of the age. For example <div id="wrapper"> becomes <div id="wrapper" class="project-5">. This allows you to then add additional styles to a theme that are specific to that project. For example:

.project-5 #header h1 {
    color: green;
    text-decoration: blink;  
    background-image: url(company-logo.gif);
    ...
}

If it works, you could make a feature request to have the code change put into the release.

This is a great idea. We are using redmine internally but would like to also expose it externally for users/clients to issue support bugs, and our management would then require that the redmine "theme" match the product theme to some extend. So per-project themes would be great.