In reality what most people incorrectly do is set their camera on automatic and hope that their camera is smart enough to know the difference. If not, then the answer becomes “Fix it in Photoshop!”. If that’s the plan, then you better be shooting in RAW format because any color temperature adjustment (in fact any adjustment) made to a JPEG (.JPG) file is destructive in nature and continual adjustment will eventually destroy the photograph completely.
If, for instance, your camera is set correctly and you shoot your photo, all is well. If it isn’t set correctly, your photo will be pushed either to the blue/purple end or the red/orange end in the process of taking the photo. This is easily fixable if you shot your photo in RAW format and destructively fixable in .JPG format. Lesson here is to always shoot in the RAW format and make all your adjustments on layers in Photoshop. This will preserve the original shot forever which can be repeatedly adjusted without ever destroying the information.
If you read the article “Understanding White Balance & Color Temperatures in 8 Steps” at the website SLRLounge it discusses these ideas and is divided into the following 8 topics. It's an excellent article for anyone who doesn't understand these concepts and a great refresher for those who do.
- Realize Your Limitations.
- Find the White Balance Settings
- Memorize the Icons
- Understand and experiment with K.
- Understanding Light Temperatures/Colors
- Memorize Common Kelvins
- Troubleshoot Mixed Lighting
- Using Gels (Filters)
This information is also discussed in the video below by Mike Browne. I find him to be very knowledgeable and easy to understand. If you like this video you can find others by him on youtube.com discussing many other photographic ideas and topics. I highly recommend his videos.