Will this be done in 4.0? Because the current one lags like heck.
You probably don't want to be using it in real time anyway rather pregenerate what you need and cache it because SwapColor like most icon operations generates a new icon which is both time consuming and needs to be downloaded by all the clients that need to see it.
Yeah, I doubt the inefficiency you're experiencing is due to SwapColor() itself. (Though perhaps it could be optimised somewhat, I really don't know.)
If you're encountering speed problems with icon procs, chances are you're overusing them. As Theodis says, you should cache your results whenever possible. Pregeneration is usually a good idea too, unless you can afford to have a delay the first time the icon is shown (which is not likely).
Redesign your game so that there isn't? =P I don't see why you'd need to be creating hundreds of SwapColor()ed icons. Beyond a certain point, differences in colour are virtually indistinguishable anyway.
If you don't mind sucking up oodles of disk space, you could pregenerate the icons once and save them out to icon files for later use. (So you don't have to pregenerate at runtime every time the game starts up; just once.) But be warned, this will inflate your RSC file something massive.
No matter how you generate them, lots and lots of icons means lots and lots of resources for players to download. This will LAAAAAAAAG your server like you wouldn't believe.
Icon procedures have been speed up, but they're still rather slow. My PC would have trouble changing shading the icon with an RGB and I'd be the only one in the world. This shows that since my PC is really crap, it'll catch that the icon procs are still rather slow. You stick 10 people and a good computer hosting, and you'll get what my PC gets.
You probably don't want to be using it in real time anyway rather pregenerate what you need and cache it because SwapColor like most icon operations generates a new icon which is both time consuming and needs to be downloaded by all the clients that need to see it.