It's easy to use the eyedropper tool to pick a color from an object ( image, video, webpage, etc.) and apply it to other objects. (This feature is only working on Chrome at present.)

For example:

Add an element to the canvas.

Click the color panel, click the + icon, and click the eyedropper icon.

Then, move your mouse to pick a favorite color. Single click to apply this color.

Voilà!