Okay but what was creeping, strange person? And what's that about riots? And he's starting to think the castes have to do with... hair colour?

People use a couple words interchangeably for the castes but, yes, some of the words they use are colors and the colors seem to match the ones that are around. (There are no blues in this coffeeshop; things attributed so far to blues have included the ability to arrange travel visas, so much money they could 'pay it off and never even notice', the allocation of child credits, and connections in the courts). 

The person whose husband shot something says 'it was red' as if this is self-explanatory; her companion certainly seems to agree. 

He will try to pay more attention for the word 'red' in other conversations.

It's not a popular conversation topic! 

" - walked right out of the alley, and when they called in greys he just vanished. There's a surveillance photo circulating but it's blurry -"

      "- yellow?"

"Yeah."

     "So what was he doing there -"

"How would I know?"

...he should not be yellow anymore, but he's not sure what to be...

...green. Seems to be the scientist or artist caste, if he's getting these conversations right. He'll pay for his drink and slip away and continue to pay attention to conversations around.

People are worried about making ends meet and annoyed about their commutes and the train crowding and wishing they could afford to get out of town for the winter. Orange professions mentioned are teacher, daycare worker, paramedic, therapist; yellow ones are secretary and software developer and auditor and journalist; green are roboticist and university professor and mathematician and photographer and novelist; blue might be the government and everybody's landlords; grey is military and police and sports; purple is retail and manufacturing and farming. 

People really don't talk about red much. Eventually - "I hate hiring reds, hate it, so we've been putting the pipe repairs off for months - we might go on vacation for  a week just so I don't have to fear the children getting near them -"

" - and then a red does the autopsy, and you watch - behind glass, of course - to get an understanding -"

Reds are "dirty things." Whom people don't care if they shoot. Got it. He slips off into an unwatched alley again and changes his hair to green...

...makes himself shorter...

...he's still unearthily pretty but he likes that and it will only stand out normal amounts.

He's not going to rush this. This world is crap; so are most others. Rushing things won't help, it was already going through crap before he arrived, if he rushes anything he'll probably cause way more harm than good. He needs to learn more.

First things first, then: he'll need to officially exist. People don't just start existing out of nowhere. He's not sure how hard that will be, it depends on how electronic this society is, whether they use paper ID or something more complex—but the existence of paper money suggests they're not too far beyond his Earth, technologically.

Hmm. If he got things right, a good place for a green to be might be a university. He zips around a corner so it doesn't look like he's coming out of the alley, then starts walking with the flow of people and trying to pay attention to anything people have to say about where one might be.

There's a conversation within range about a university but not about where to find it.

He looks for the speakers. Are they green?

They are!

Good so he could plausibly ask—" Excuse me."

"Hmm?"

"I'm a bit turned around, where can I find—" and he names the university they were just talking about.

Take the S train six stops and walk along East.

He thanks them and looks/hears for the train station.

Train station! Incredibly crowded, with every color but red.

Including blue? He once again pays mild attention to all conversations around him.

Yep looks like blues are not important enough to avoid public transit. There's a more expensive car up front where they mostly sit, though. 

" - and the execution's on Friday but I don't really know if I want to go, and I think the kids had probably best stay home -"

" - you'd think they could set a price for immigrant visas, even if it was outlandish, and then there'd be some hope -"

" - gave money to a red girl and I think I know what that means - couldn't bring myself to report him but I sure reported her -"

Death penalty. How incredibly charming. What was the crime? And what's that about visas and a red girl?

Crime was trying to strangle her during a domestic altercation, sounds like. 

Visa person is upset that there's no allowance for legal immigration to this country where he wants to go to university. 

Woman caught her husband sending money to a red girl and reported the red girl and left the husband.

Ah huh.

She's now assuring her friend that she didn't take a single thing from the house not even her great-great-grandmother's earrings and showered for eight hours once she'd gotten to a hotel.

...he'll try to reserve judgment until he's figured out whether there's some biological basis for their worries.

Friend soothes her that they'll take care of the red girl right quick and she was right to leave and very even-tempered not to set him on fire first really.

Ugh. How do these people even exist if they hate their plumbers so much.