How could color blindness be prevented?

As it's genetic, the only way to "prevent" it is to have a child with a person who does not carry the relevant gene.

EDIT: Also color blindness can be caused by a deficiency of Vitamin A and retinal diabetes so making sure you have a healthy intake of Vitamin A [liver, paprika, cayenne powder, chili powder, red pepper, sweet potatoes, carrots etc] and sugar/starches can help prevent it.