<font> tag is a depricated tag and should not be used. If you are using a wysiwyg editor you will probably have to rely on their capabilities to color your text, but if you have those turned off, or can switch to an html mode (and assuming your editor doesn't strip html), you should use something like:
<span style="color:blue;">sample text</span>
Also, there's another approach. If you have my Textile mambot installed and published, you can use textile markup in your content. This is like wiki syntax and to have red text you would put: