The change of sky colour at sunset (red nearest the sun, blue furthest away) is caused by Rayleigh scattering by atmospheric gas particles which are much smaller than the wavelengths of visible light. The grey/white colour of the clouds is caused by Mie scattering by water droplets which are of a comparable size to the wavelengths of visible light.
Mie scattering on thin clouds during sunrise, a bit later
Celeste River is a river in Tenorio Volcano National Park of Costa Rica. It is notable for its distinctive turquoise coloration. The source of the river’s distinctive turquoise color is not a due to a chemical species but to a physical phenomenon known as Mie scattering, a scattering of light occurs when the particles causing the scattering are larger than the wavelengths of radiation in contact with them.