All my frozen foods I put into a little cup with some vitamins and let it thaw in that for a couple hours before I dump it in. Just be careful and feed a quarter of it first before dumping in the whole cube. But basically just throw the cube/piece in the tank. Things like beef hearts and bloodworms can make a huge mess if not eaten. Might wanna turn your filter off too. And I wanna know if they see in color or not too...
This is the answer I found.
Most fish see in color. "Experimental evidence indicates that many shallow-water fishes, if not all, have color vision and see some colors especially well," says the Encyclopedia Britannica, "but some bottom-dwelling shore fishes live in areas where the water is sufficiently deep to filter out most, if not all, colors." These bottom dwellers do not respond to color differences when tested in shallow waters.