If you're exploring various color palettes and moods for a piece, Photoshop has a secret tool to help you speed through the process. It's actually not a secret, but many illustrators simply don't know about it. Unlike other color overlay techniques, this command will replace colors based off of their value. This means that your highlights will be treated differently than your shadows, etc. To properly use this technique you'll need to know how to create a gradient in Photoshop, though it's not discussed in the video. Luckily, gradients are a very old feature for Photoshop and Illustrator, so it isn't hard to learn about them on the internet.