What's up with the sky

That makes complete sense. Good thinking. It's not so much that the clouds are liquid, because everything reflects light. Clouds just happen to reflect light well.

Red sky at night night is a sailors delight. Red sky in the morning is a sailors warning.

Light pollution from mercury vapor street lights is what turns the sky at night pink to orange when there is any water vapor above a metropolitan area. When street lights were sodium vapor lights the light pollution was blue -white and much more annoying. The second thing I noticed when I got back to New Orleans the first time after Katrina almost months after Katrina was the total lack of light pollution from the Lakeview area, and the severely reduced light pollution from Orleans parish from my house greater New Orleans. Last year when I went home for Christmas was the first time that light pollution levels from Orleans parish were almost equal to the Pre-Katrina levels, but the street lights have been changed in the Lakeview area so there is still less light pollution than there was before Katrina. Unfortunately, there are still a lot of sodium vapor street lights in south shore greater New Orleans. I've lived south of Oklahoma City most of the time for almost 31 years, so I've seen the change from sodium to mercury vapor street light light pollution.

http://www.lightpollution.it/worldatlas/…

http://www.skyandtelescope.com/community…

http://www.skyandtelescope.com/community…

http://en.wikipedia.org/wiki/Mercury-vap…

You are actually amazingly close to right. It's not necessarily the fact that there is liquid present or not, and it's not reflection, but scattering of light (Rayleigh scattering, the reason why the sky is blue, is the primary factor). When light hits tiny particles in our atmosphere, those particles can 'scatter' certain wavelenghts of light more than others, some of those others may be partially absorbed or reflected, but the overall color you see is the average of all the scattered wavelengths combined.

I'm willing to bet that most of the time, the pink clouds are seen near the horizon close to sunset or sunrise, or are 'underlit' by light pollution from Earth in the direction of a nearby large metropolitan area.

Another thing to think about, is the rods in our eyes are very good at picking out the wavelengths of light closer to the red end of the spectrum, especially in low light. Ever notice how the ripe strawberries are easier to identify at night than the unripe ones? At night, your eyes will see the scattered pink easier than say, blue or violet.