The Color Picker is divided into two tabs — Spectrum and Palette. To use either one, select a layer of your image and click the color dot in the palette that opens. If the Layers palette is not open, click the three stacked squares in the lower left of your browser window.
The Spectrum tab offers a high degree of control over color selection:
If you know the Hex code of the color you want, type it into the box next to the color dot (It looks something like this: #123456.)
If you want to choose a color manually, drag the circle on the rainbow bar to pull up different color ranges in the selector square. Then choose the specific color in the square.
The Eyedropper helps you choose exactly what color you want from another part of your image. Click the Eyedropper and hover over the desired color. Click on the color to apply it to the selected layer.
The Palette tab includes curated collections of colors that work well together. Choose a palette that works with your design, then click one of its colors to apply it to the layer you’ve selected.