After wearing your baby for a long time, you may notice that his skin is reddish on places where the fabric was in a bulk. This does not mean ateries or blood flow are bothered.
Be careful that he has no pressure points on his groin (for instance, when baby's in a cloth diaper and you do a Vertical / Seated Cradle Carry).
Denim trousers and other thick fabric clothes can also cause the skin to redden because of the seams.