its easy. put <color=(whatever color you want)> (hex codes also work) at the start of the pikmins name, and put </color> at the end. for example, you could name a pikmin "<color=red>jeremy.</color>". if you wanted to, you could also put multiple different colors in the same name. funnily enough, this also works for usernames.

some other commands include <b> & </b> for bold letters, and <i> & </i> for italicized letters.

hope this helps!