well I discovered this...
at least for the visual effect

I used 2 RichTextBoxes...1 hidden

when Coloring was to occur (like when ENTER was pressed)
It would copy text to the second window...do the color then give it back to the first...then it just flashes

also look into getting the current line that is being typed on.
so all you should try to color is the current line

Download the code to my VBBrowser (link below) the code is a little hard to follow but what you need is in there...

the code window in the browser will color each line after enter is hit. it is about 90-90% accurate
a few bugs to work out still but...hey... no time