Steps in correcting color photos in overall adjustment stage

1. Visual check the color shift and brightness of the photo.
2. Use Level tool (hold option key) to determine the detail highlight and detail shadow areas.
3. Slightly brighten the photo to better determine the color shift if the photo is way too dark. Pay extreme care not to push any color channel (RGB) to higher than 250 in detail highlights.
   
4. Start adjusting the highlight color with Level by checking the white (or neutral highlight) area.
5. Adjusting the mid-tone color with Level by checking the mid-tone gray area.
   
6. Adjusting the shadow color with Level by checking the neutral black shadow area, be very careful with extreme shadows because when a color is very dark, it could appears as a neutral black but actually it might not.
   
7. When adjusting colors, better take multiple small steps rather than big adjustments. Big steps could easily become over-correcting. In most cases, it is always better to be close to enough rather than too much.
   
8. The opposite of RGB is CMY. Increasing the additive color means decreasing the corresponding subtractive color. For example, if a photo shows Yellow (Y), increasing Blue (B) can cut down Y. However, if a photo is too Blue, especially among the highlight areas where you can’t cut down B by moving the highlight slider of Blue channel, you will have to move the other two primary color (R+G = Y) to add yellow in order to cut down the highlight Blue.

Yellow (Red plus Green) is the complement of Blue. Cyan (green plus blue) is the complement of Red. Magenta (red plus blue) is the complement of Green.