Permutation parity
As shown on the left, there are 5 pairs, if one couple of that 5 pairs do the Interchanging PAIR Move, then one couple of the 3 corners with color as shown on the left will also interchange position.
That is, the permutation parity of the 5 pairs meshes with the permutation parity of the 3 corners with color.
That is, only do the Interchangine PAIRs Move, it will not change the linking of the permutation parity of 5 pairs and the permutation parity of the 3 corners with color as shown on the left.
Demonstration
Watch the animation on the left to feel the above explanation