Before you type anything, click on the color you want to use. It should work. While I'm typing this, I see that it's blue. If I go down too far when starting a new paragraph, it will be black again. So, I go back to the last paragraph and then try again. Hope this helps.
Tell me what you are doing. If you are just posting on the "Quick Reply" that will always be black. If you want to post your own thread, click on "New Topic", then choose your color and click on the color. The go down to the page and start typing and it should work.
If you are just responding to a post, like this one, click on "Post Reply", choose your color and click on it, and then type. Is this what you are doing?
When you choose your color, do you click on that color name? You have to do that for it to work. I haven't had any problems with it.