By mixing Red Green and Blue you can create any color you want. This is usually done by passing the LED light through some sort of diffuser such as waxed paper. Have a look in the individual LED section for full specs. on these LEDs.
If you only require a one or two LEDs we are probably not the best place to get them since you will need to pay a few dollars for shipping. Stores such as Radio Shack also carry a selection of LEDs. They are much more expensive but this might be the way to go if you only need a few. Here is a link to a White and Blue LED from Radio Shack. Keep in mind that the mcd number relates to how bright the LED is, the higher the number the brighter. We only carry LEDs that are very bright.