The color of a lake in satellite view depends on the satellite's viewing angle (which depends on the satellite's trajectory and the lake's location), the angle of the sun (which depends on the same things plus the time and date the image was taken), the weather, the satellite's sensors (false color is a thing), and how the images are processed before publishing. Overall I think it's almost impossible to estimate the "true" color of a lake from public satellite images, even if you used all pixels instead of just one.