Hi Sandy,
That will not affect the group related results, that option is to return groups as results.
However, there is a way to restrict the search to a certain forum content only, using a hidden custom field filter. To do that, follow the instructions below:
1. First, let’s find the forum ID, to which we need to restrict the results. To do that, open the forum in the editor, and look at the browser address bar.
2. Then on the Frontend Search Settings -> Custom fields panel, make a hidden filter, with this configuration.
3. Save the options, and clear your site cache.
Now the live results should be only topics/replies from that specific forum only.
If the color changes does not show on the front-end, you might need to clear all layers of site cache you have (page, minify, CDN etc..). If that does not work, then there might be a 3rd party stylesheet overriding the colors. In that case, can you link me to a page where I can look at it? You can also tell me which sections you want to change, and I might be able to suggest a custom CSS code for that.