Advanced selections: the Magic Wand tool
The Magic Wand tool is one of the best selection tools because it selects objects based on their tones; plus, it's so easy to use. If I use the example on an image featuring a blue sky and a dark landscape, clicking on the blue sky with the Magic Wand tool will inevitably select everything that is blue, but if the sky fades from dark blue to light blue, as most skies do, you might find that Magic Wand only selects a band of color, not the entire sky. This is because the pixels that you click on represent a certain shade of blue. The tool will not automatically select every pixel that's blue. Its sensitivity (to the range of blues, in this example) is controlled by the Tolerance slider. The default value for this is 32, so if I were to increase the tolerance value to, say, 100, it would grab a lot more of the sky. If you set it to the maximum value, 255, the tool will select everything in the image, regardless of its color.