Tieflings rarely form their own societies but when they do there is a strong sense of pride in their appearance. After all, any village that consists primarily of tieflings is one that is protected by a demonic which they likely also worship. While there are mixed societies that enforce a degree of shame upon tieflings there are plenty more that accept them as just another race. Demonics aren't necessary evil. They're just far more ambiguous than the angelics and always have some cruel streak. So long as you stay on their good side, everything works out in the end. As tieflings are tied to their vices rather than to malice, per se, they can even be more laidback and at peace than those of other races.
• Tieflings provide those dearest to them with a favor, called a 'promise', which is a symbol of their oath to never let their darker nature get in the way of their friendship. This might be a lusty tieflings' vow to never cheat on a partner or a lazy ones' earnest promise to never shirk their duty to a liege lord. A tiefling who disregards or breaks such a 'promise' are punished by any tiefling who learns of their betrayal. After all, the sanctity of the 'promise' is one of the reasons why those of the other races can trust a tiefling more than most.
• Tieflings take great pride (or shame) in their family tree and will either know the demonic source of their lineage or be actively investigating it. If a tiefling refuses to tell you about their lineage, it means it is a shameful one and must never be brought up again. A tiefling who wishes to discuss their lineage with another tiefling will normally drop hints but will be subtle about it so that the other tiefling doesn't feel backed into a corner.
• Tieflings, as a rule, take great pride in their homes. It doesn't matter if the home is a cozy cottage or a brooding gothic castle. It will be well-tended with not a cobweb out of place. The tiefling will attempt to make it all look quite effortless, of course. The only tieflings who lack this nesting impulse are those who are too consumed with wanderlust to bother. Having said that, even those tieflings are likely to take pride in their backpack and the design of their sleeping bags. They are also most likely to spend a bit more on a quality inn room.
• Tieflings pick up slang and swear words in other languages quite readily and prefer to sprinkle them in to the rest of their dialogue. This isn't an instinctive thing, merely a social one. Some tieflings will even go so far as to create a pidgin language out of bits and bobs from other languages so that they can use it with other tieflings.
• Tieflings tend to be fastidious eaters and are easily put off fouled food and unhygienic locations due to their rather sensitive tongues. On the plus side, they also make exquisite wine tasters as they are generally quite capable of tasting every note in a wine bouquet (apologies if I use the terminology wrong as I am no wine connoisseur.
A yuki community is bound by ties of pledges, oaths and promises that must never be broken. They are quite pragmatic about their settlements and while they have a higher threshold for cold climates they build their homes so that they can be easily warmed and protected from extreme weather events.
• Yukis will avoid making promises, even incidental sideways ones, if they can help it as they take all such things to be binding. This can be very disconcerting to members of the other races. It's not that a yuki doesn't intend on performing the action (such as attending the party) but if they make even a subtle promise to do it then they are honour bound to follow through. If they don't believe it strictly necessary for them to brave extreme weather to attend the party, or crawl their way there if they have a sprained ankle, they won't make the promise. Yes, they take promises that seriously.
• Yukis therefore tend to be noncommittal in their speech. "I would like to be there...." "That party sounds like a nice thing to attend...." "It would be nice to see your performance...." This noncommital manner also affects them in other respects with a more passive manner of speech and the invention of a variety of ways to avoid explicitly saying "No".
• Even the poorest Yuki will aim to maintain a sleeping space for guests in the event of an extreme weather event. It is considered immoral to refuse an honest guest refuge, even if the weather isn't particularly bad outside. This sleeping space could range from a bit of floor and a blanket to a full bedroom suite.
• Yukis are raised to carry a whistle or a horn about their person so that they can more readily signal others when they're injured. Such objects also have a handy side effect of scaring away most (though not all) lesser predators due to the sudden blast of loud noise.
• Yukis consider white to be the colour of death due to their ranks of camouflaged assassins and ambushers who keep their villages safe. Those in a white dress, for example, can hide among the snow using their innate protection against the cold before rising up against the enemy. Therefore white is a funereal and a war colour. The yukis also take great pains to prevent them from being stained while committing violence and have mastered the skill of getting out of the way of an arterial spray.