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theTicket
I have quite a bunch of human/humanoid OCs with dragon counterparts, but all are from fantasy settings.
I too go for the secondary as their hair color because of the mane, but sometimes the dragon I chose will change the originally intended human design a bit. Genes don't really matter for me, since I'm collecting gem gened dragons (with very few exceptions). All dragons have gjinkas in the profile.

Thorill was set as an old battle hardend warrior, so I knew he'd get armor and a sword. Also a fatherly figure to another OC, so I kind of made him a friendly old guy. I wasn't sure about his skin color, so eventually the primary leaked into the design, when I had to decide on it for a commission.

Xarilesia here is that "queen bee"/"high school queen (tm)". Again originally set in a fantasy setting, she loves jewerly and picking on other people.
Her colors fir her skin and hair color.

Ysalya is currently the only dragon with a human design, where the dragon was first and then her design was developed. Basically everything was taken from the dragon: her dark skin tone, hair and eyes. Yellowstarfire did an amazing job of designing her gjinka.
Personality wise she's rather shy and quiet.

I bought her first, then named her after my old tauren druid from World of Warcraft and then ended up designing her gjinka design. Her primary is the skin color, secondary the clothes (dress), tert color is her apron and the apparel and accent I used are all reflected in her clothes and accessories as well.
As for character creation: you can try picking 3 traits to describe a character. This little tool helped me a lot for dragons, where I didn't have a set character yet:
click here
My characters are full of tropes and clichés ;)
You can have a "good guy": a valiant hero with a dark secret or just have him be the prince on a white horse every person dreams about. So the prince can be nice or very self absorbed, while the valiant hero could be really torn on the inside and is trying to do good because they want to attone for something. Characters always start out as something and then grow over time into something totally different. Xarilesia for instance: I came to love her. She's the adversary (opponent) to a very good and nice character that I designed and it was fun to write out someone who's mean for a change.
I usually make good characters, because I like to be nice and don't like mean people.
Character ispiration could come from people you admire, you like or don't like.
Many of my characters are from my own stories and settings or pen and paper chaacters, so they have an ongoing story line, but others are "just there". They often started out as remembrance dragons from world of warcraft.
Typical questions for chracter creation:
1. where does the character come from? - their upbringing may make a difference at how they react to other people or situations.
2. what do they like / dislike in general? - coffee vs. tea, vanilla ice cream vs. chocolate and so on
3. how do they view society?
4. what do they fear?
5. Any disabilites? They could have a hunch back or a bad leg or be blind in one eye.
6. how do they look?
It's also a question of "What do you intend to do with the character once you've created them?"