Complex sentence: Even if there is no bulk motion, random thermal motions of the particles will give rise to momentum flow, so the terms (green) represent isotropic pressure, and the terms (blue) represent shear stresses.
Split into simpler sentences: Even if there is no bulk motion, energy might be transmitted by heat conduction, and the conducted energy will carry momentum. Random thermal motions of the particles will give rise to momentum flow, so the terms (green) represent isotropic pressure, and the terms (blue) represent shear stresses.