What about you' and 'how about you' are both idiomatic expressions used to ask someone for their opinion or response, but they can also have slightly different implications depending on the context in which they are used. 'How about you' is often used in situations where the speaker is expressing a preference or making a suggestion, and wants to know if the other person shares their opinion. It can also be used to express empathy or solidarity, and to show that the speaker is interested in the other person's feelings or experiences. On the other hand, 'what about you' is often used in situations where the speaker wants to know if the other person has any additional information or thoughts on a particular topic. It can be used to prompt discussion, gather information, or encourage participation. Both phrases are often interchangeable, and the choice depends on the speaker and their preference.