Colorizing is a good thing to know using photoshop. It's one of
the basics and if you don't know much about it yet, then maybe this
tutorial will help you.
1. First open your image. Mine here is Liv Tyler.
2. Then make a new layer (Layer > New > Layer or click
Shft+Ctrl+N). You can also make a shortcut my clicking the small icon
at the bottom of the Layers dialog box:
3. Then choose the gradient tool. And choose a color that you want to
colorize your image. Mine is #7590C7 .
4. On your new layer, fill it with color by using the gradient tool.
You can use two colors or multiple colors with pre-made gradients (you
can find sites that offer them). And then on the layer dialog box,
adjust the layer options from normal into color mode. You can
also choose other options like overlay, sof light or hue. It depends to
you. It's better if you try a lot of things and by that you can
discover more ways to colorizing images.
5. Now my Liv Tyler picture will look like this:
6. I adjusted the opacity settings to 80 % but it always depends to you
on how you would like it or what would look best. I added some
brushes and texts and this is my final image. It's not that great and I
know you could do better. But the whole point of this tutorial is
teaching you how to colorize.