One of the most important things that outdoor photographers must overcome is the notion that you need plenty of light to make good pictures. And "plenty of light" invariably translates as a "bright and sunny day".
Soft, pleasing light can enrich many colorful subjects. Overcast lighting often makes colors more vivid than direct sunlight and is more likely to reveal delicate details as well. Muted light offers minimal contrast, so scenes arenít marred by deep shadows and glaring highlights.
The soft, even illumination cast by a white sky is especially flattering for photographing people, and a thick cloud cover mimics the studio light produced with soft boxes and white umbrellas.
The diffused sunlight of an all-white or all-gray sky is wonderful not only for photographing people but also flowers, pets, close-up subjects, waterfalls and streams, intimate landscapes, and colorful architectural details.
Beware of White Sky:
While an overcast sky filters the sun to create pleasing light, an image containing a big expanse of stark white or light gray, featureless sky will often be disappointing - the brightness can make everything else in the photo look dark in comparison. Hereís the usual "rule": Skip grand-scale scenics that include boring (read: white or light gray) skies.
Oh sure, there are exceptions to the no-sky rule, but not many. Either leave a white sky out completely, or severely reduce the amount of it.