Someone said I have a “Depressive overtone” they would not tell me what it means though, so what does it mean?

It could mean that the person who told you this feels you don't exhibit lots of upbeat, happy behavior.  You are more prone to sad or serious moods and discussions.  If its just one person, don't get too concerned, often people see themselves in others.

If you feel the person is correct, try thinking about more happy things in your life which you can talk about and feel good about.