Step 21: Apply A Gradient Fill Layer To Add Color

Click on the New Fill Or Adjustment Layer icon at the bottom of the Layers palette:

And select "Gradient" from the list:

When the Gradient Fill dialog box pops up, click inside the gradient preview area at the top:

This will bring up the Gradient Editor dialog box. Click on the gradient swatch in the top left, the black to white gradient first, and this will make sure that both colors on either side of the gradient have their opacity set to 100%:

Then set your gradient colors to whatever you like. I've set the color on the left to a reddish-orange, and the color on the right to a yellowish-orange:

Exit out of the gradient dialog boxes once you've chosen your colors.

Step 22: Change The Blend Mode Of The Gradient Fill Layer To "Color"

With the Gradient fill layer selected, go back to the blend mode options in the top left of the Layers palette and change the layer's blend mode to Color:

The image is now colorized with the colors from the gradient: