The basics of community property teach you that all income earned in marriage belongs to the community unless it is an inheritance or a gift. These gifts and inheritances are considered your separate property, even if they are received during the marriage. But, some gifts might not actually count as your separate property.
California also has rules about "transmutations," which are contracts between spouses to change the character of some property. In order to change community property into one spouse's separate property, there needs to be a signed writing clearly evidencing the intent to change the character of the property. So, when your spouse buys you a car as gift for your birthday, writes you a note saying "I gift you a car. Happy Birthday," and signs the note, the car is still community property, because there was not clear intent to change the character of the property.
So, unless you meet the qualifications for a transmutation, a gift between spouses during marriage is unfortunately, not considered a gift for the purposes of characterizing property.
Maria E. Crabtree, CFLS