I planted two different lilac trees in my yard. One of them gets dark purple flowers in early summer and in the fall It surprised me when it's leaves began to turn a beautiful dark red.I would love to read up and learn more about this tree however I lost the card to tell me what it is called. Is there someone that can help me?

Welcome to the NGA
I am not a lilac expert, but that may be a little leaf lilac?
Sometimes called a Korean Lilac ?

No, the leaves show it belongs to a group of lilacs call the Preston lilacs, of which there are many named varieties. One might be able to guess which one when it shows its flowers. Hopefully, a suggested name would jog your memory. Preston lilacs bloom in early summer, Korean lilacs (and most other lilacs) bloom in spring.