Profiles for 5D and Mark II

😕 Can someone please help me understand this PROFILE THING!!! I have been using my MarkII and have loved my images........I just got the 5D and I have not changed anything and the results are aweful! Skin tone is gray.....If I am using more that one type camera on a job is this going to create a problem? How do I get the same results from the 5D? Is the camera profile under the workflow, Color management causing this? I really am not understanding this!!!