A lot of hormones are transfered during birth and this can affect the genitals and overall skin look of a child. The tip of the foreskin (if this is what you are referring to) is often red at the end. This is normal variation for many infants. My son always has a reddish tip in comparison to his shaft skin.
The only time you need to start worrying is if urination problem occur, you get pus, fever or excessive swelling (and sometimes even these things are par for the course-- swelling can sometimes be smegma pearls, etcetc)
I wouldnt worry about it

If you feel you really need to put something on there to at least try and really do feel something is wrong, a simple barrier diaper rash cream will work. But, like I said, if it stays reddish, that could just be your son's normal look...as it is with mine.