why is it when I take a photo outdoors, with the flash off, in broad daylight that the sky always comes out white in the photo?
You’re blowing your highlights. The sky is much brighter than the subject. Blowing out the highlights is bad, since you can’t recover any of the detail in Photoshop. Either turn on your flash (best method); adjust the exposure setting so you underexpose (get a blue sky and a dark subject) and then brighten the subject in Photoshop; or reorient yourself so the source of light is at your back or the sky isn’t in the picture at all.
The camera is simply recording light. Light has a thing called dynamic range, which is the brightness of everything from the blackest black to the whitest white. Each increase in brightness is referred to as a “stop”.
Whether you’re shooting film or digital, you are limited in the dynamic range that you can capture. With film, print film can give you about 8 “stops” of DR, slide about 5-6 stops. A DSLR shooting in RAW can capture about 6 (although with the right post-processing that can be extended). A digital p&s will capture less than this, but off the top of my head, I can’t remember exactly what. The human eye can see a much greater DR than what a camera can record.
Hope I’ve not confused you yet.
When you point a camera at a scene, the cameras meter reads the varying levels of brightness, and generally averages the whole scene to what is referred to as 18% grey. This is a neutral midtone, that exists roughly halfway between the whitest white and the blackest black. It then sets the exposure accordingly.
Now, when shooting in broad daylight, especially in the middle of the day, the DR that exists in the scene is greater than what the film/digital sensor is capable of recording. This is known as a “high contrast scene”. Happens all the time, especially in Taiwan. What this means is that, it’s impossible to capture all the colors as they look to the eye - the brightness range is too great.
Generally, we don’t take pictures of the sky only. So, with a high contrast scene, we point the camera at our subject, which is usually much less bright than the sky and the camera wants to record this as a midtone. If the sky is more than 1-2 stops brighter, it will get “blown out” and end up looking white. The blue of the sky is simply too bright for the camera to handle.
If you really desire a blue sky, point the camera at the sky, half press the shutter button to lock the exposure, then, keeping the shutter half pressed, recompose and shoot. You’ll get a blue sky, but chances are everything else will be too dark.
Hope this helps a bit.
Don’t you just hate that. Start typing a long answer to a thread with no replies, and then by the time I finish and submit the post, 2 people have already answered it in fewer and easier to understand words. 
Using flash in daylight can actually reduce exposure by speeding up your shot – assuming you are shooting in Program or Auto mode. It can also be used [in daylight] for fill lighting for shadow areas. Easier way to reduce exposure would be to set the ISO lower… as opposed to using the flash to reduce the exposure.
Have you tried using a polarized lens filter? They’re excellent for blue sky shots and work great for reflections shots too… Should cut down a bit of your white sky prob…
Rule of thumb…don’t shoot outdoors betweem the hours of 10AM-3:300PM. The shadows and colors will suck. The light’s too bright and people will squint. Watch a movie…when do they shoot? Early morning and late afternoon.
Your explanation is great, much better than the one I linked too! :bravo: