well the "color of the sun rays" always stays the same, yes. so when you take pictures in bright daylight - set WB to daylight.
city lights at night... well, the sun certainly is not shining, is it. depending of the lightsource (probably the citylights themselves) you have to set WB to either tungsten or artificial light. this way (and only this way!) they will look the same as you see them.
see here: Understanding White Balance
My conclusions...
After doing alot of investigations i got to these conclusions:
Using DAYLIGHT WB means you get on the computer screen the same color chroma as you see it with your own eyes for real. This means street lights will remain orange, tungsten lights yellow, etc....
the camera simply keeps the RGB data as is... no chroma difference.
By setting the camera to manually WB - for example: Using a peace of white paper to calibrate WB under orange street light at night, will make the peace of paper look white, as it was observed in daylight (altough our eyes see it as orange in reality at the time of photographing), while other natural lights, like clouds under moonshine, will get artificial blueish shift. And that's what i DIDN'T wanted to happen
I want to see everything on the computer as i saw it exacly in reality. If that paper of white car had a yellowish look, it should be kept that way for me. That's how my eyes saw it... I can never get better results of a night image showing city lights from far (with, or without moonshine) without applying daylight WB!
(Using AWB or any other method of manual evaluation might shift the beautiful dominant orange lights to artificial color)
Don't forget, that our eyes evoluted to the chroma of the daylight. So by using daylight, and only daylight, you can keep the original colors (and this means white papers become orange under orange light).
I know that WB (other then daylight WB) should be applied to make white stuff look white as they were illuminated by daylight. This usful for me when taking indoor portrait shots of people under yellow tungsten light, so their faces would be looked as i was taking them under daylight.
