You could use javascript. something like,
[glow=red, green, 00FF94]test[/glow]
And have the javascript get a string using {option}, then seperate by commas and then it would have 3 colors, THEN, it would apply thoose 3 to the {param} tag and print the final result back onto the webpage :D Shouldn't take too much time.

:D Feel free to release this mod yourself.

Too lazy hahahah already working on other mods /:

I honestly just hate javascript... I try to avoid it as much as possible these days.

install and it worked but one thing , when i post a glowing text , it posted at the bottom why not on the top of the post, how do i fix this?

What version of vBulletin?

v4.0.3

need a link to your forum where you have glow used in a post.

Cheers. Installed.