There are a few things you can do to help when selecting by color in Photoshop. The first is to use the eyedropper tool to select a color and then use the color wheel to choose a hue. You can also use the Hue/Saturation slider to adjust how much of that color you want to see. Another thing you can do is use the selection tools to select specific colors. For example, if you want to select all colors in a document, hold down the Option key and click on each color in turn.
