Wiring and heat loss

Duct seal is a gray paintable putty that stays relatively soft. If your shingles are painted, it would blend in pretty well after painting. I would just leave the duct seal as is if the shingles are natural or stained as it's a commonly used sealant and would look entirely normal. I suppose you could make or buy some sort of a cover if it bothered you to look at it.

I'd still consider using foam to seal inside the wall, with duct seal on the outside.

Janet,
As Mark suggests, foam inside the hole if you can neatly. Stuff with fibreglass if you're concerned about foaming all over the place. Or tape the area around it. Foam is not for the faint of heart. A small hole with a cable through it might be tough with spray foam.

I would either use the seal he talks about-it does stay pliable for just about ever, but holds itself and the cable pretty good as far as air and water infiltration. You mold it around the hole-getting some inside to give it some grabbing power.

Or, I'd use a complementary colored Urethane caulk. That stuff sticks to everything-no problem with wood or wire. Start the caulk inside the hole and carefully move it around the wire, sealing the opening. You can do a little artistic "molding" of it. Turns your fingers black if you get it on you and don't clean immediately with denatured alcohol.

Those wires etc should be held in place so they don't flop around. There's some cable clamps (find a phone guy etc and beg him for some). Hex drilling screw with a tab that goes around the cable. Aluminum-so no rust. Much better than staples. Make it neat, straight and run it where it doesn't look like [JOBSITE WORD] if you can.

How big of a hole are you talking about?

Dig this janet. They fixed the Preview feature!
They eliminated it at least on this reply.
Pure genius.