For 3D on a TV screen or computer monitor red/green (or red/blue) tinted lenses are needed.
The image for one eye is tinted red and the image for the other eye is tinted green/blue. These two images are then overlaid to form one image for broadcast/streaming. You'll know that it's 3D as objects will have a red tinted ghost to one side and a green/blue tinted ghost the other.
3D films are projected and can use polarised filters to achieve the separation between the eyes. This means that the colours can be completely natural.
As you need two images it's not normally possible to convert an existing film to 3D. There is one case when it works - when you have a lot of movement in the scene. The brain can be fooled into thinking that the image is 3D by displaying the current frame to one eye and the previous frame to the other. If the camera is moving then objects nearer the camera will apparently move further than objects farther away between successive frames. By presenting the "this frame" and "last frame" images to each eye separately the brain will reconstruct a 3D image in exactly the same way as if the two images had been taken by separate cameras at the same time.