The newer LED/bulbs are direct replacements. I no longer use the standard bulbs. All color LEDs are available. Warm white bulbs are for those who must have the old fashioned look. I can honestly say that I have more than 125 of these in use at this time. I'll be adding another 75 next month. One thing you'll notice right off is the lack of heat generated per bulb. My train room used to feel like I was setting in front of my heater. I hardly used my a/c unit last summer. Once you get used to the blue/white glow you'll be hooked. I'll be changing out all of my locomotive lights as well.
highrailsteve, I have a friend who sells these cheaper than anyone I know of. My email is in my profile. I'll gladly give you his contact information.