Well first off, you have to make a style in order the change the color of some text. That is what CSS is for. With that in mind the correct process of changing the color of some text would be to create a style that defines the color you want, select the text and then apply the style to it.
There are many ways to create a style, but you can go to the Format menu --> CSS Styles --> New...
In the CSS window, choose the type of style. Either redefine every instance of a particular tag (not what you are trying I would guess), a class (if you want to reuse the style more than once), or an id (if it will only be used once). Then give it a unique name and choose where they style should go, in this document only or in an external style sheet to be shared between multiple pages.
Once created, then go back and select the text and in the properties inspector choose to either apply your class or id. If you redefined a particular tag, make sure that tag is around the text you choose (for instance, an h2 tag maybe).
of course there is always the way of direct formatting, as follows here as an example:
<span class="Stil5" style="color#996600">