The main complaint about microfiber applicators is the that they absorb too much product. Microfiber applicators make coating product application easier, quicker and more efficient, but coatings typically have a lower viscosity (not as thick - flow easier) so they soak through the microfiber to the sponge, wasting valuable product.
The solution to this problem is the Saver Applicator. A layer of a hydrophobic material has been added between the microfiber and sponge. This prevents excess coating product from soaking through the microfiber into the sponge.
They are two-tone only to differentiate them from the standard microfiber applicators, which don’t have the product saver hydrophobic layer. The two sides function exactly the same.