Computers can take green or blue out of a shot and overlay images of another source. Depending on the equipment used and the skill of the production crew, this technique has been used for years in movie making. As technology advanced and became less costly, it is available to almost anyone today, The less expensive editing equipment has problems around ill defined edges, such as a feather duster or furry wind sock on a microphone. To a trained eye it's fairly easy to see but to most unsuspecting people it's totally believable. With MSM covering Biden, look for it. Reflecting light from a green or blue screen can often bleed into skin color. If Biden has a slightly off color look from the background, that's probably the reason.