Out of the three regular peeps we see in NC, Least Sandpiper is the easy ID due to the yellow legs when you can see them. Mud on the legs can complicate things, but usually it is pretty straight forward. That being said, the plumage can vary greatly and I am still trying to learn the differences.
Here is a photo from early in September, where the bird is still very colorful. Also note the relatively long bill which is not typical for Least.
Here is one of the more typical small billed and less colorful birds.