Brilliance LED has dedicated mr-16 color lamps for this purpose. Diode create the colors, not a lens or filter. 3.8w units come in blue, red, green, and amber, as well as warm and cool white. Will fit the fixture you mentioned.
Here is the link: http://www.brillianceled.com/MR-16_3.8.pdf
Also this lamp comes in 15, 30, and 60 degree beam patterns. Hope this helps.