Kingbright have some 5mm RGB leds. The white diffused are available from
RS Components for about $13 each. There are also some water clear ones
for $21 ea. Price has probably changed, I'm quoting from an April 2003 to March
2004 catalogue. Tenrod in Sydney also carry them.
LF59EMBGMBC water clear, and
LF59EMBGMBW white diffused.
There are LESs with three colours combined in one unit. By varying the
current to each colour, you can get all the colours of the rainbow.
Easier to pulse-width modulate them to obtain varying brightness and mixing.
You could use a micro.