Colorizing
This is similar to the gradient overlay tutorial but it will instead teach you how to do ONE color. If you have any queries please email me =D

1. Choose your image, I'm just going to use a Neopets background image
2. Duplicate your layer by right clicking >> duplicate layer
3. Set your foreground color to what you want the colorize to be then Edit >> Fill >> Foreground Color
4. Set your duplicated layer mode to "Color"
Voila! You have successfully colorized your image!
Duplicate your colorized layer and play around with blending modes.
Suggested Blending Modes
-Color Burn
-Lighten
-Vivid Light
-Overlay
-Screen
~Chels