So you start with your image. Get a paint brush - I like to use it with the same color that the thing is I am changing it's color. Then you need to set that layer to color in the blend mode drop down menu (next to opacity by default it is set to normal). You will have to be meticulous and color with the brush everything that you want to change.
Then make a hue/sat adjustment layer and create a clipping mask. Set your hue/sat adjustment layer to the colorize option at the bottom and then start seeing it change!
*Keep in mind that you want it to look realistic so you will have to adjust the hue to set your color then the saturation and lightness to make it look real.
*With the darker colors (red) you will have to make a duplicate layer of your painted background and set it to blend mode multiply and lower the opacity in order to make it look realistic.