as said previously, yes they are LED's as standard. because they're classed as side repeaters, it would be an MOT failure and another excuse for the bobby's to pull yo over if you changed them to a different colour. I'd be guessing anyway that it will be a circuit with soldered-on LED's since they're designed to last longer than the car...in other words, i don't think you'd be able to change them. unless you rip the whole lot out, but it sounds like a hell of a lot of work for what it is.
i think they look cool anyway

its usually mercs etc that come with these sort of mirrors (more recently some VW's and toyota's etc) but the honda ones are by far the brightest!