As others have pointed out, RGB naturally eats up three times as many controller channels than if you went with one color. Someone on another thread mentioned that IL has stopped manufacturing the translucent buttons as sold on LizardLick and Paradise. I have no idea if that's true but I also have no reason to doubt it. *IF* you want RGB then you would either want something frosted/translucent white like GroovyGameGear's Electric Ice buttons, or you'd go with clear translucent buttons....
Now, looking at both LizardLick and Paradise, they still have the colored translucent buttons available but both show the clear ones as out of stock. If IL is no longer manufacturing them, that might mean trouble. LizardLick is also closed to new orders at the moment, while they catch up on backorders according to their site.
GroovyGameGear sells NovaGem translucent buttons with the LEDs integrated into them but there's a tradeoff, they're about $6 (vs. about $3 for the other ones) but they do save you the time and hassle of adding your own LEDs. Also, they're showing out of stock right now too.
Ultimarc sells some illuminated buttons, but while I love Ultimarc for lots of other products, I'm not a fan of how those buttons look. Are they flat topped? I like the concave ones I'm accustomed to.
I am hoping to still get my hands on some clear IL buttons if anyplace has any in stock (or restocks), but not at an inflated price if they are indeed discontinued.
Funny, I'm saying all this and I haven't actually illuminated my panel yet. I've bought a bunch of stuff but ended up deciding to rebuild the panel completely, so adding illumination is on hold while i select parts and lay out a whole new panel. Since I personally love the blue on black motif I associate with MAME, my buttons will NOT be all RGB. I have nothing against RGB, but for now all my player buttons will be illuminated blue. The trackball will be RGB, as will the start buttons, and possibly some illuminated trim. For the administrative buttons, I've got some thoughts I won't give away just yet.

Does anyone know if GroovyGameGear has electric ice buttons available with the player 1 and 2 start icons? I messaged Randy but haven't gotten a reply yet, and it's not showing in my sent messages box so maybe it just got lost.