Is it possible to let the users choose (select) the text color while creating topics?
When it can be included (if this option is not included)?
Please take it as a request from me if this option is still not in your to-do list.
I'm sorry, but we are not planing to create this feature and this will not be added into our to-do list.
If you want to stand out some topic from others, you can use the wpForo – Topic Prefix & Tag Manager addon: https://gvectors.com/product/wpforo-topic-prefix/
The different colors of titles will confuse other UI / UX components, so this is a conflicting feature, and we will not add it.