In the pinhole camera, light from various parts of the scene will have "interesting" effects as the different things in the pictures will have different contrasts. But there will be nothing "wrong". I don't believe it is common to use a filter on the cameras.
Originally Posted by clothesontheline
The variable contrast feature in the paper is designed for the darkroom. For example you change the color of the light from the light bulb that you use to make that final print. They make sets of filters that go from rich magenta/purple to strong yellow.