Jumping in with no comment about Plegridy .. but I inject copaxone and have by far the most trouble with the leg sites.
I've been on it since Feb 2016, and I notice the blue-grey pigmentation that JJ mentioned (that is, after the angry red spot goes away 2-3 weeks later). It is very pronounced when I first get out of the shower, then fades a bit with room-temp skin.
I, too, have worse injection site reactions on my legs than my abdomen. I have been attributing that to my extra padding around my tummy (at least it's good for something!!).
No red spots or freckle-type marks though.
Cheryl
I've heard of blue-grey skin pigmentation changes that can happen with some DMD's but not brown shades that i think of when i think of freckles, so i haven't a clue if freckles could be a med reaction sorry.
Just a thought but you could try taking a close up of your planned injection site freckle free and then incremental pics to show the development of pigment changes, so your neuro has the visual information to understand that these freckles only turn up after injecting and were definitely not there before...
Cheers.......JJ