You will have trouble with both of those. WIth HD, Color will definitely be tough. It will work although it might be slower. Doing one clip at once or something in Color you actually wont notice, but thats extremely tedious and takes forever. Both color and motion will run slower than normal but they will work. Motion will get extremely frustrating to a point. I have gotten frustrated from both of those programs running slow with 8 gigs of RAM.
Regardless definitely doable. Another question... Do you have firewire ports on your macbook? If im not mistaken the new ones dont have those and FCP is not designed to be run with USB externals.