Display entries related to Category Field I'm sorry If this has been answered before, but I couldn't find any answer that would work for me. Maybe I'm just treating category fields the wrong way and I should be trying to do this with tags.

Basically, I created a category group called colors. I also have several categories like green, blue, red...
I assigned URLs that look like mysite/colors/red, mysite/colors/blue.

All of the colors point to the same template colors/index.html

How can I display only the entries in craft.entries.section('news') that are in the "red" color category when I visit mysite/colors/red?

Thanks in advance.
You want to use the relatedTo filter. See the docs here: https://craftcms.com/support/entries-related-to-category where category is your last URL segment (eg red).

Just a quick addition... if your category URL for the category group matches what you've used above mysite/colors/red and you are using the category template for that group then you will have a category variable already to use in the relatedTo filter.