What does es usted una persona alegre o triste mean?

Are you a happy or sad person.

This is talking about a state of being, not if you are now happy or sad. It is asking if you as a person have a positive or negative outlook on things.

The Spanish Word ES is "to be", in this case "Are" but it is a permanent state.

The Spanish Word ESTA is also "to be" (are) but it is a temporary state.

Are you happy now

Esta usted alegre ahora

Are you a happy person

Es usted una persona alegre