If you're really brave the GBA Afterburner CAN be used with a Game Boy Color...I've done it, but it required some serious Dremeling to the case. Basically, you have to first pull the clear plexi cover off the front of the case (it's glued to it, but an eyeglass screwdriver can remove it) and dremel out almost all of the plastic underneath.
The trick to the whole install is to put the Afterburner in upside-down, with the LED at the top instead of at the bottom (the front fresnel lens surface of the screen must still face outward!!!). If you cut enough out, it can be made to BARELY fit. There are two sacrifices, though: there are six screws that normally hold the GBC case together, and you have to sacrifice the one in the upper left (looking at the screen). It doesn't seem to present a structural problem as far as I can tell, but you might want to stick a rubber stop or something in the screw hole to keep dust out. The other thing to go is the power led (who needs one when the whole screen lights up?) It winds up behind the Afterburner, and prevents the clear plexi from fitting back on properly. I simply desoldered mine, but I suppose you could solder in a lower-profile one.
There are several gotchas to the install:
1. Power/ground connection to the screen: by installing the screen upside down, there is no room for the tab with the solder pads. The solution is to bend them back behind the LCD, but there is a potential problem. The flexi circuit is made of two layers and bending them tends to separate the two, breaking the connection and rendering the screen useless (the LED won't light up). This happened to me, and my solution was to GENTLY take an X-Acto knife and scrape away the insulating layer on the top and bottom of the tab, then make solder pads so I could solder the power/ground wires separately (so that it didn't depend on a join between the two layers). The idea is, ground goes on top, and power goes on the bottom (before both were on top, and power went through a layer join).
2. The GBC has little to no spare area for the resistor. The idea is to AVOID a short-circuit from the resistor leads. My solution was to shorten the leads on the resistor and connect the resistor to pin 1 on the cart port (Vcc) and bend it back on itself so it ran through the little plastic loop that runs from the cart port to the edge of the circuit board. I then used a thick, solid wire to connect the other end of the resistor to the dimmer pot, which I mounted on the side of the unit next to battery compartment. The solid wire's purpose was to act as extra structural support for the resistor. The aim here is to prevent the resistor from shorting against the cart port pins or anything else.
3. The overall tightness of the install. Everything fits so tightly, that the clear plexi in front of the screen (that is normally glued to the GBC case) doesn't like to stick tightly at the corners (the brass casing of the Afterburner screen LED tends to push it up a little). The issue here is dust. You want a tight seal to prevent it from getting in. I haven't really tried to look for something appropriate yet. I'm reluctant to use super glue in case I need to get in there to get dust out at some point. I don't suppose anyone has an idea what might be appropriate?