As we begin to utilize blend modes the more power we get to add depth and life to colorized images.  

There are at least 8 different ways to do everything in PSP and that goes double for colorizing.  

Here are some comments on a couple of methods to liven up our efforts.

Colorize basic steps

-open your grey scale image
-make your layer palette visible
-create a new layer named PAINT
-set blend mode to OVERLAY

-make your control palette visible
-grab airbrush and choose settings
-hardness and Steps set at 1
-brush size 15-30 (size as needed)
-opacity and density at 100 (adjustable)

-choose a couple of colors to play with and spray some color on your new layer.

Jump right in and glob it on without trying to be too nit-picky perfect.  

We need to see how our sprayed-on color looks and behaves as it interacts with the image below.

Remember, slopped over areas can be eraser fixed later with more precision than trying to paint perfectly now.

Be on the lookout for those areas where the colors may not be grabbing to your satisfaction.  

Generally it's preferable for our b&w image to be toward the light side, however colors can't overlay (grab) on pure white ... so some white areas may need to be darkened before colors will take.

Select the resistant pure white area and use color adjustments from the colors menu to darken slightly or ...
-create a new layer over a "too light image"
-flood fill it with color
-reduce opacity down on new layer
-merge flood filled layer with the "too light image"
-proceed with creating the new layer for the actual colorizing

Cleaning up your paint job

ERASER TOOL
steps and hardness 1
opacity and density 100
size ... you choose

Try to keep the size of the eraser as large as is practical for the bulk of cleanups.   

Go back later with a smaller eraser and dig out those leftover little crevices and crannies the big eraser couldn't reach.

Why?  Bigger erasers with a soft edges
(hardness at 1) often produces a smoother easier more controlable edge.

I am quite fond of the eraser

If (when) we screw up, we just press the right mouse button and that little sweetheart replicates and redraws whatever got erased.

A tool with it's own get outta jail free card built right in.  Holy cow, let's use that eraser whenever we can.

Blend modes for colorizing

Color interacts to colorize, but expect somewhat weak results in many images
Multiply grabs well and darkens often requires some opacity reduction to look real
Screen is going to overall lighten everything for a more dreamy/pastel look
Hard Light & Overlay: both quite useful, often producing the same results ... but not always.
Soft Light: very usable under some circumstances but seldom a first choice

For most regular coloring we can generally ignore the remaining blend modes in the layer palette.