Nice Senegals! The close-up pic of their faces is very nice. The only thing I am a little nervous about is the slightly discolored spots on the one. Have you treated them for any illnesses or parasites yet? Perhaps someone could comment as to what the spots are. It may also be trauma from running into something.
in regards to the substrate: I would recommend putting them on sand because they tend to enjoy resting on the bottom.
As others have mentioned, darker (black or red) substrates can bring out greens, or you could do a yellower substrate. I currently have a mix of black and white sand. Just please do not use gravel, because they can and will eat it...this can potentially cause intestinal blockages. Would also recommend some flat rocks and plants or hides(without sharp edges) to make them more comfortable.
Welcome to the club!