red black tree and 2-3-4 tree isomorphism
It depends what you mean by isomorphic. Indeed a black node with its (zero, one or two) children corresponds to a 2-3-4 node (with 1,2,3 keys and 2,3,4 children). The basic operations on the two types of trees are really different but translate quite well. 

There is a single difference in symmetry: there is only one type of 3-node (2 keys, 3 children), whereas in a red-black tree the red child to the black node may be at the left or right side.