HTML only works if you import it. The forum takes in BBCode only but BBCode allows HTML with a certain tag, [HTML] I'd think. BBCode uses [] instead of <>.
Also, what would a span do? If anything, wouldn't it be <color> or <p color>? Spans are better with CSS formatting as opposed to specifying an area in HTML.
<p color="Green"></p> is the best way to do it, but if a span tag works, go ahead.
[COLOR="Yellow"][/COLOR] is the BBCode format of colouring.
That's a coding lesson for today, unless you already knew it..