I put a blue one in. Looks kinda cool I guess. Like it was said previously, it's only 4 bucks or so. You can get blue, amber, green, red, purple, white, etc. Platypus gave me this link, but I found mine at a shop where I live.
http://www.mojomusicalsupply.com/cgi-bin/mojotone/scan/co=yes/fi=products/rf=sku/sf=prod_group/se=Electronics/op=eq/sf=category/se=Pilot%20Lights/tf=brand