Okay, this tutorial is a bit advanced, so if you're a beginner in Photoshop, this may not be for you.
If you use Paintshop, I'm sorry, I can't answer questions. I've never used it. But, I'm sure that most of the steps I do in tihis tutorial are possible to do in Paintshop, so you're in luck. ^_^
WARNING - this tutorial is image-heavy...so if you're running on a slow connection, well...that sucks. I'll try to be as descriptive as possible if it takes forever to load the pics...they're high quality.
Het asked me to do this after finishing my
Paloma fanart (which I'm really proud of) and so I'll share my erm, techniques!
I tried to make the colorization pretty different from the original picture, so...yeah. Okay, finally, here's the tutorial!!
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TARA'S COLORIZATION TUTORIAL!
For this tutorial, I used a high-quality image for easier coloring. The model in it is KD Aubert, and I got the picture from www.cutiecentral.com (GREAT resource, esp. for actresses of color)

Here's the original image. I resized it so it wouldn't be too big. This is basically my finished product:

To start, I prepped it for coloring.
Create a new layer, and use the dump bucket to fill it with white. If you don't have the dump bucket (like me), in the file toolbar, select Layer > New Fill Layer > Solid Color and select white.

Then, go to the layer palette, and change the layer's blend mode to color, like shown above.

You can start coloring here, but I prefer not to, and prep it some more.
Go to Layer > New Adjustment Layer > Levels in the file toolbar. A box will pop up.
Make sure the channel says RGB.
Under the input levels, put 6. 1.42 and 255. In the output levels, put 25 and 255. If the end result is too bright for you, simply lower the opacity in the layer pallete. I left my opacity at 100%, and I got this:

Now you're ready to begin coloring!
I work with a layers technique. You don't put all of your coloring on the same layer, and you work up. So I did her skin first, then her lips, then eyes, then makeup, then the silver on her jewlery (well, gold originally) and then the jewels on her jewlery. All of these got their own layer, just in case I wanted to adjust the opacity, change the blending mode, etc. It makes it all easier. It also helps to name your layers, lips, eyes, etc. I didn't, but it can help from confusion later if you're doing a complicated color job.
I used the color #63380A for her skin. The layer was set in the color blend mode and set on opacity 100. I just colored over her skin and erased the parts that didn't need to be colored. You don't even have to do that, because if you're planning to recolor it (like her lips), then the color will change anyway.
Here's what my coloring of the skin looked like:
As you can see, there's some spots, I could've erased and stuff.
After that, I created a new layer and started on her lips. I used the color #9D1111 and the layer was under the color blend mode.
The lips were pink and I was trying to go for red, (bear with me on this) so I duplicated the layer, and changed the copy of the layer to the Overlay blend mode. That way, it looked red.

That's what it looked like after I duplicated the layer and all that.
So, the lips are done, and I moved on to the eyes.
(remember to create a new layer!) I wanted to choose an unusual color, so I picked purple. The exact color I used was #760ECE, and I...colored her eyes in. Instead of setting the blending mode as color, however, I picked overlay and set the opacity at 52%.

So yeah, that was simple. Next was the eyeshadow. I don't know what possessed me to give her purple eyeshadow, but it's what she has, so...yeah. If you want, feel free to choose whatever color you want.
I didn't want the shadow to be a vibrant purple, more a muted color, so I used #90808A as my color. I basically slopped it all over her eyelids and then set the layer as Linear Light.

That's my weird choice of shadow.
After that, I decided to do her jewlery. Since I wanted it to be different from the original, I picked silver. I wanted it to look more metallic than the black and white coloring that was already there, so I picked color #C2C2C2 and set the layer as color. Then I colored all over it.

That's the jewelry after I finished.
Then I wanted to match the jewels to her eyes, so I used the same color (760ECE) for her jewels and set the blending mode as color.

After that, you're pretty much done unless you want to add more detail like the intricacies of her jewlery, etc.
If you want, you can keep going and add effects like this:

I copied the original layer of KD, and went to Filter > Blur > Gaussian Blur. I set the blur to 4.0 and then set the layer to Overlay. (This is one of my oldest tricks, I do it all the time in most of my fanarts)
I then touched up her lips a bit, and then added a pattern on top.
Voila!! That's all. You can try out different things with different colors and blending modes if you'd like. If you do try it out, I'd like to see your finished product!
If you have any questions, feel free to reply and ask and I'll try my best to help!