Yay, you've made a good choice! They are not a great beginner's bird, but you probably already knew that. That aside . . .
Are California quails flighty (like really flighty? And how much?
That depends! I have some that were six weeks old when I got them and after three years I wouldn't say they're very flighty anymore, but they're not super cuddly either.
On the other hand, the ones I raised from chicks are a year and a half old now and are pretty much glued to my collarbone or my shoulder whenever I'm working. My boyfriend and I can't sit down in the same room as them without getting all quaily. My face is full of feathers as I am typing right now. Aside from treating me like a giant heated quail bed, my female quail is tame enough that she's sometimes willing to lay eggs in my hand.
Here are the things I have done that I think contribute to making them tame and calm:
* They mostly spend their day in my home office which is where I spend most of my day
* I hand feed them all of the time. The little ones have been eating from my hand since they hatched, so I didn't really have to teach them anything. The older ones were resistant to eating from my hand when I first got them, but I eventually learned to coax them by only giving them the most delicious treats by hand like celery leaves and mealworms. After a while they became willing to take boring food like poultry crumbles from my hand. I tried to make a habit of hand feeding them at least once a day and it really paid off.
* I'm very gentle when I do pick them up, though they generally don't like being picked up. It's easier to get a quail to come to you by teaching it its name and calling it. Associate this action with food. The true way to a quail's heart it through his proventriculus. ;)
* Having lots of space to roam around and nice little nooks to hide in when they need privacy makes them feel safe and secure and can help keep their stress levels low.
* Moving gently and gracefully around them and not making too many sudden loud noises or movements will help keep their vigilance at a minimum.
I highly recommend raising them from eggs for maximum tameness/minimal flightiness, but be aware that they are difficult to hatch, especially if you get eggs shipped. If you are shipping eggs, you may want to buy three times more eggs than the number of chicks you intend to hatch. Also make sure to buy from an aviculturist and not a game bird ranch, as game birds who are bred to be hunted are bred for quantity, not for genetics, and can suffer from serious health problems. An aviculturist can offer you the offspring of their most beautiful, tamest, and healthiest birds.
Are California quails more 'colorful' than bobwhites?
You can obviously see how lovely the males are, and even the females, who have dusty brown feathers in photographs, have lovely sparkly iridescent feathers in the sunlight.
Also how loud is a California quail compared to a bobwhite quail?
My quails are mostly super quiet, but your mileage may vary. As babies they were all kinds of noisy, but as adults they only ever have anything to say if they are eating something really tasty, watching an interesting YouTube video, someone was hanging out too close to someone else's girlfriend, or a quail or human they liked was not in direct line of sight. The aggression and rally calls are the only loud and annoying sounds they make, and they are generally rare and short lived. All of the other quail sounds are soft and happy and cute.