Short form: Please don't talk about his dye job; he knows it's bad. Not likely to speak to others unless spoken to first (there are exceptions). He's really nice, just kinda spacey. Long form:
First thing's first, his hair. The last thing Kieran wants to hear upon meeting someone is a comment about how bad his dye job is or being asked if he's planning on getting a haircut soon. It's not like he's self conscious about it, he's just a little annoyed from hearing the same thing from every new person he meets. (Meta: asking questions or making comments is still welcomed it won't make me immediately back out dw)
While Kieran's definitely not the most outspoken person, he isn't asocial either and will gladly respond to any friendly interaction he's given. Sometimes he'll initiate a conversation if he finds something about you particularly interesting, (i.e. eating something he think looks good, listening to music, or wearing something he thinks looks nice on you) but is quick to retreat if he thinks you're growing annoyed with him.
If Kieran's reactions/responses start growing dull, don't worry, he's (hopefully) not growing bored with *you*, more so with the topic or just starting to drift away, more likely. It's a great queue to change the subject to anything, whether or not he likes it. He doesn't have the confidence to tell anyone to their face that he doesn't like something they do so he'll let you talk while he drifts further away until you snap him back into the conversation or he actually does grow bored with you.