Simple plug in, add dropdown menu to wysiwyg editor

I’m writing a very simple plugin.
so far when I type
<blue>example</blue>

would be replaced with

<p class=”blue”>example

this goes on for red, green and yellow.

This is just an example, what I want to do now is this:
instead of typing <blue>…</blue> I’d like to have a drop down menu in the default WP editor (no tinyMCE) so when I select a portion of the text and chose on optionfrom this menu it would be wrapped in the tag Ispecified.

Have I been clear? I hope so.

Any help or pointing to the right direction would be greatly appreciated, just keep in mind I’m not a programmer.

Really thanks to everybody