If they just have an extra "channel" in the eye in addition to the standard three, a RGB image would look the same to a tetrachromate as it looks to us. However

If they just have an extra "channel" in the eye in addition to the standard three, a RGB image would look the same to a tetrachromate as it looks to us. However, the rest of the world would look much more nuanced and colorful to them, hence the RGB image will look flat and colorless, like say an image where the red channel has been removed looks colorless to us. It's basically impossible for us to comprehend how rich and colorful the world looks to e.g. birds which has tetrachromatic eyes.