Anton, I tried the same.
For question n. 1 I concluded that actually it's not possible. Class TreeRenderer  seems to  be waiting for further refinement  (see empty methods such as getIconBackgroundIcon).
For the second question: this is what I did for customizing node styles (removing underlining from links and changing hovering):

.p_OraTreeRow A:link {
    text-decoration: none;
.p_OraTreeRow A:hover {
    font-weight: bold;

You can apply furthe restyling. I know that these should be "private" selectors, but they are the only possible customizations for trees I could find from sources.

-- Renzo

Kunze, Anton wrote:

I'm using the trinidad tree and navigation tree components and I have to
customize the look and usability. How can I change the node character
(triangle) or replace with an image?
How can I mark a selected entry with a given background color?

Best regards