In general dimmers don't work on LED's. They are current activated as opposed to voltage driven like incandescent lamps. As you try and dim them, you will find some will be brighter than others. The chances of you getting a dozen or so identical lamps, is not too good. LED dimmers are not resistors, they are Pulse Width Modulators, similar to how the alternator regulator works on later model Jeeps. If you are good with a soldering iron, you can build a PWM, however, you may have some interference issues with your radio.
Soo what to do? If you just want to change the color, Sharpie indelible markers are supposed to be quite effective. I've only used red. You may also try a search for "lamp condoms or balloons" these are the OEM boots that fit over the bulb.