Font tags are now deprecated, meaning that they aren't used any more and will cause validation errors. Many legacy pages still contain style information in font tags. It is possible to resolve this by replacing with style tags instead.
CSS styles can be overriden by browser settings whereas font tags can't, therefore styles are much better for accessibility. In addition, because the browser can't override font tags, it's not possible for users to make changes if they have a high resolution screen and the font size is too small to be legible, or if the text cannot be displayed at all because the user doesn't have the right font.
By default Cute Editor converts font tags to span tags. <font face=times color=#ffffff size=4>your text</font> would be replaced with <span style="FONT-SIZE: 110%; COLOR: #ffffff; FONT-FAMILY: times, serif"><font size=4>your text</font></span>.
If you still want to use font tags, you can set Editor.UseFontTags property to true.

Online example can be found in http://richtextbox.com/test/UseFontTags.aspx 

 

Regards,

Eric