Why is the Mantis brown

By "combat", they mean man-to-man combat, not ship-to-ship combat. Basically, Mantes make good raiding parties or security guards.

To teleport your crew members back:

1. Make sure your teleporter is active (after using it to teleport crew members over, it will take a while for it to reset and be usable again).
2. Make sure the crew members you are trying to teleport are standing in a room, not entering or leaving it. (If they're busy fighting someone that's fine) .
3. Click on the bottom of the two teleportation icons.
4. Click on the room in the enemy ship which holds your crew members.