They can't? I should watch that series again... Anyway, good point, but of course they can't, because the phaseshift forces truly massless particles (like photons) into a state of quantum entanglement.

That means photons hitting them, create an entangled twin that only exists long enough for them so see their surrounding. The "original" photon however just passes through making them invisible to others. Energy from the surrounding is used to create the twin, cooling the surrounding shortly. However, since the twin is immediately reabsorbed (and the entanglement broken), you basically can't detect the effect.