How do you know when you've got the correct colour balance in post-production (i.e lightroom)? To explain further, I have several shots where the same rocks or stones are grey in one shot and brown in others. Similar comment for sunrise photos with red/orange hues.
There are two interpretations of "correct colour balance", so I'll need to cover both possibilities.
If we are talking about getting the colour balance correct so that we record the scene as it actually was, then the easiest way to achieve this is to use a grey card at the capture stage. A grey card is balanced to reflect the same amount of red, green and blue light (RGB value), which gives it a neutral (colourless) appearance. A grey card is also designed to reflect exactly 18% of the light which strikes it, which makes it appear as a tone exactly half way between pure black and pure white. However, the amount of light being reflected is irrelevant for colour balance. The important thing is that the subject is reflecting equal values of red green and blue. So you could just as easily use a white piece of paper you have lying around in your bag, or the back of an instruction manual (as long as there are no colour texts or pictures on it). Just place whatever you decide to use in front of your lens (doesn't matter if it is in focus or not) but make sure it is being illuminated by the same light source that your subject is being lit by. For example, if your subject is being lit by an early morning sun but you are standing in the shade of a large mountain, you cannot do this technique. If, however, the sun is shining on you and your subject (or you can easily walk to where it is shining) then place your card in sunlight and take a test shot. Now remove the card and take the shot you will use for editing. When you have your images loaded into Lightroom, go to the White Balance fader and to the left of this you will see a pipette tool. Grab this and drag it onto the grey card in your test shot. It will now render this area as having equal RGB values and the rest of your scene will now be correctly balanced. All you need to do now is copy the White Balance and Tint values to the photo you took without the card. It is important that you don't leave too much time between taking your test shot and your actual shot, as the colour temperature of the sun will change very quickly at dawn and dusk. If you leave more than a couple of minutes between shots, then the results may not be accurate.
So that is how to get the correct white balance to render the scene as it naturally was. However, the light at the time you were taking the photo may have been very orange, which can desaturate greens and blues, so you may want to achieve the "correct White Balance" to achieve a result which looks more pleasing and natural, rather than accurate to the lighting conditions at the time. For example, if you were taking a photo of the Quiraing at dawn in June, it should look amazingly green, but in the first few minutes of the day when the sun is just above the horizon, the orange light will suck all the greens out of the landscape and you end up with a very brown looking image. In order to get things back to how they should be in your mind's eye, you'll need to cool things down with the White Balance fader. There is no exact answer as to how much you do this, as every photographer's opinion will differ. Basically you just need to gently push the White Balance fader to the left until the image suddenly looks too cool (blue). Now you know you have gone too far, so back off a little and you should have something which appears as you want it to. If you find that some areas (such as the sky) go too blue before the areas being lit by the very orange sunlight appear to be correct, then ignore the blue areas for now and get the sunlit areas looking good. Once you have achieved this, go to the Colour tab (although being American they have spelt it wrong!) and press the "all" option at the top of the tab. This will now display 8 colour faders. Go to the blue channel and push the saturation to the left until the blue areas look good. Voila!
Hope this helps