If you want to quickly pick the color from an image or a shape on the canvas, use the eyedropper tool.
It looks like this:
In Figma, you can press "i" on the keyboard to select the Eyedropper.
Once it's selected, hover over an image or a shape on the canvas and click to sample the color. This will populate the color into the color picker.
If you first select a shape you want to change the color of, clicking to sample the color with the eyedropper tool will shape the color of the selected shape:
Pro tip: We can take this further and "scrub" or continuously sample the image with the Eyedropper by clicking and dragging it across the image, trying different colors in context to feel out which one we like:
Now let's take a look at a more advanced timesaving use-case.
If we use the Selected Colors panel in Figma in conjunction with the continuous sampling using the Eyedropper tool, we can save a ton of time changing the color across a lot of elements: