Colorization++ - Potatoe's

[Terrapin Bound]

Masking has been my most common method.
A new layer for nearly every color, then add a mask. Then select the area, color it, and mask as necessary where you went out of the lines.
For multiple colors/shades on one layer, I'd adjust the areas of the layer as necesary, using lighten/darken/hue/etc.
Soften the edges of the mask for a nice color-to-color / layer-to-layer blend.
Images tend to get very heavy with layers using this technique, but also allow for a lot of precision and flexibility.
It's a lot of work.

Alternately, I've used a pad.
Add new layer, color with the pencil, erase the mistakes, etc.
I never got real good with pressure for crayon width, but I can see where it is much easier once you get used to it. You can carve a very fine edge with pressure/width adjustment, and it saves the great trouble of making a selection, and adding a mask layer.
But like others, it's a real estate issue. I shall endeavour to persevere.

I never quite figured out how to translate that old tutorial to PS. A step that was so simple in PSP seems so cumbersome in PS, that I must be missing something. (Duplicating a mask layer and applying it to another layer).
The tute was more about selecting fine detail with a mask layer, than masking in general.