I've always heard that a characteristic of the paint is to be "nutty", especially if they have a blue eye. Is this true? How do you choose a paint?

Conformation and soundness of horses,

http://www.angelfire.com/sc2/petswelfare/horses/sound.html

A blue eye could be localised scarring of the surface of the eye usually due to a healed ulcer. It is not a problem if only a small area is involved and the scarring is off-centre, but if it is over the pupil the horse may be blind in that eye. If the scarring is extensive enough it makes the whole eye appear blue. This is not to be confused with the blue eye caused by a lack of pigment in the iris, as in cremellos horses.

I have had registered paint horses over the years and NONE of them have been "nutty".
I've also heard many yarns about horses with blue eyes. And they are just that yarns. Or you could call them old wives tales. While it’s true that some horses are more active than others, the color of its eyes or body has absolutely no bearing on its temperament. Rather the behavior is the result of poor training.

The way to choose a horse, no matter what breed it is - -is to begin with answering a few questions…. what you want to do with the horse, do you want a horse for the show circuit? Or just something you can ride around on in the neighborhood. What riding skills do you have? Who else in your family will be riding the same horse? And what type of riding skills do they have? You need to match your riding and handling ability with a horse of equal ability.

For example…(just an example) If you know nothing about dressage, but the horse does…. it is above your riding ability. A horse that “knows” more than you can become easily frustrated and will be perceived by you as un-cooperative and “nutty”. By the same token a person who is just learning about horses should not have one that is untrained for the same reason. Lack of communication between rider/handler and horse.

The next concern should be its health. Choose one that is in excellent condition. But before you make that final decision, have a vet do a full check up. After you have made a decision at this point, its time to check other factors. How well are you able to groom, lead, tie to post, saddle up, and trailer the horse of your choice BEFORE purchasing?