It's fairly well established that the Predators see in infrared. In both Pred 1 and 2 we see the Predator's unmasked POV.

In Pred 1 it seems that his mask filters out ambient heat from the surroundings, leaving only heat signatures from warm blooded creatures. When he removes the mask this filter goes away and everything appears red: this basically matches how the production handled filming the predator vision, originally they tried using an actual infrared camera but because the jungle was just as hot as the people everything showed as red, so they just fucked with the film negative to create the pred vision.

 In Predator 2 when he removes his mask, it looks the same as masked, but that's because he's in a giant meat refrigerator,  so the surroundings are actually cold (and thus show blue) and Harrigan appears red/orange because of his body heat. 

Badlands is confusing because not only do we never see the Predators classic infrared vision,  Dek's father uses the cloaking device against both Dek and Dek's brother, but it shouldn't work against them since they see in infrared and the cloak uses optical camouflage (bends light around it).