Check: ? -> relics

You have 2 slots for offence relics, 2 for def and 2 for production.

And for more info visit:

http://wiki.plarium.com/index.php?title=Relics

The open slots aren't labeled. What category do scouts come under? Your answer doesn't help that much.

Have you read your relics description and wiki, JOHNL1055?

You can have only 2 active relics of each type (2x offence, 2x def, 2x production). That's why you can't activate any other relic of the same type.

Scouts come under def relics.

Color indicates type: offence, defence, production.

There are temporary (3-7-14 days) and permanent relics.