You might try asking here
Cosmetic Mods
You didn't specify the model, but generally the LED is soldered in a little board at the end of the battery and it is very small. You'd have to remove it and micro-solder another back on to actually change it.
There are other ways to tint the color towards what you want... like removing the cap (if it is colored in particular) and using a marker to add color or something else to tint it (gel, artist stuff, colored semi-transparent tape, whatever). Whatever you do, just don't short out the board.
P.S. Oh, and if you glue the cap back on (say... on a 510), remember it is part of the safety stuff... make sure it can "blow off" again if the battery vents.