4 month old male Chihuahua puppy with "freckles"?

Hi guys!! I want to start off by saying I love this site and you guys are great! A few months ago, I got the oppertunity to foster a pregnant chi and then her pups once they were born. She had 3 pups and all were healthy (at first). 2 have since gone to great forever homes and 1 earned a permanant spot in my home (and heart) This little boy has had a rough start. When he was 1 month old, he ended up with puppy strangles. He has recoverd from this and has gotten a clean bill of health from our vet. My question is, he was born pure white. At about 1 1/2 months, he started showing light brown spots. Now he has what I think of as freckles all over his body. And they seem to be multiplying! Should I be concerned about this or is this just his normal markings? Thanks so much for any info!!