Color is characterized by the axial component of the polymer stress tensor.
It can be observed that the polymer stress is not uniform over the filament cross-section during stress growth. Since the fluid elements move radially inwards the cross section, this shows that the velocity compensation technique does not yield ideal extensional kinematics there. We find that the fluid elements near the free surface experience larger stress and average molecular extension than those near the axis of the filament, due to the fluid's memory of non-ideal kinematics at the early stage of stretching. It is only at the end of the stretching that the polymer stress becomes uniform. If the upper plate is stopped then, these profiles will relas uniformly as they would after pure extension.