If you updated your opencart store to latest version 1.5.5 or 126.96.36.199 you might have noticed that in the admin Html Editor (for product description, category description, information pages content and so on) the Font size selector and the color selector are missing.
Its because in version 1.5.5 opencart has updated the html editor it uses (ckeditor) to it's latest major version. And in the latest version , things are a bit different (certainly looks better) and has more functions but they are not inlcuded in the standard built used by opencart. You could go to the ckeditor site and create your own ckeditor built with all the functions you want (they have a wizzard for that) or you can add the missing blocks as extensions to the standard built. Here is more info on that: http://forum.opencart.com/viewtopic.php?f=20&t=96797