As i have a lot of control codes in my scripts i usually forget what colour code is for what, so when it comes to adding things, i have to /echo the whole line to see what codes are what.
Maybe the script editor could be put into a "preview" mode whereby it just shows the effects the colour codes have on the line.
so
msg $chan 4coloured bold $nick and underlined text
would show as
msg $chan coloured bold $nick _and_underlined_text_
Just a quick ability to preview it before editing it again. Maybe make the window read only when its in this "preview mode". Or even just a little window underneath the main script editor with the currently selected text in it.
Or an edited version of "Courier New" to show the control codes as a little B or a little U or somethin. Not sure of the legality of that tho.