Complex sentence: It owes its color to hemoglobin, to which oxygen binds, deoxygenated blood is darker due to the difference in color between deoxyhemoglobin and oxyhemoglobin.
Split into simpler sentences: It owes its color to hemoglobin, to which oxygen binds. Deoxygenated blood is darker due to the difference in color between deoxyhemoglobin and oxyhemoglobin.