That's some dramatic light sources!

But what I mean is that you should map out the entire image in one go. Not only the light sources but the surfaces they hit. You can do so roughly at first, and if you work on a Multiply-mode layer you can do so very quickly.

Below is a colour-mapping a did as an example.



This is working on a Multiply-mode layer (starting from my previous Conan-colouring). MyPaint is a better program than GIMP for this kind of work in my opinion, since one can work much faster using something like the Modelling2 brush.

In GIMP you can work with the paintbrush and a fuzzy brush or the airbrush (whichever you are more comfortable with), but use a low opacity (in the 30% range). Set up keyboard shortcuts for changing the opacity. MyPaint allows you to adjust the lightness/darkness of the hue with a keyboard shortcut - not sure if GIMP allows that. Of course, a pressure-sensitive tablet also speeds up the process. The above example took maybe 30 minutes (it's also very rough as a result, but that is the point).

The goal with the map here is to establish some sort of balance to the painting. For example, I started out making the curtains red, but found that since Red Sonja has red hair it would disappear against the red curtains behind her - so I shifted them towards purple. If I had done each individual element separately it would be annoying to have to redo it once reaching that point. But since this is so sketchy it's cheap to just try another hue to see if that works better. Same goes with the blue of Conan's mantle and throne, they must both differ from the yellow of the lion and the colours of the curtain and Red Sonja's hair (which is also why I opted for something other than golden bracelets for Conan - it would meld into the lion's colour).

I didn't spend any more time on shading Conan here, but did a first example for Red Sonja. I had her lit from the front, so she could probably be even darker. There is nothing stopping you from imagining a fourth source of light off the edge of the image to the right if you want her to be more interestingly lit (the line art tells us nothing about such things so we are free to toy around). Also note the shadows on the ground, something not covered at all by the line drawing.

As you see the dark areas (such as the night sky in the background) are also fully filled to get a feel for just how the image will be balanced.

You could relatively easily churn out several such crude colour/shade maps to test different colour combinations and shading setups - as long as you remember to work sloppily and don't worry too much about filling the lines you should not feel too bothered about throwing away your tests and try something else.

Once I was happy with the rough mapping I would continue to further establish the shadows, increasing contrasts with deeper shadows and brighter highlights, all on a Multiply layer. I might go over the image with a Color-mode layer to help make surfaces coloured by the light sources (see the blue area of the throne behind Conan's head for an example of picking the yellow of the torch and dabbing with low opacity using a Color layer). Color mode covers the lineart though (at least to an extent), it should be used with more care.

This is still the prep work anyway. What is going to take the most time here is the detailing, such as the individual stones of the floor, the jewelry and strands of hair etc around the entire image. But by that point you'll at least have a good feel for where the image is going and you should not have to stop and ponder if a colour or shadow belongs or not.
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Griatch

PS: I personally prefer to keep the line art intact, using primarily Multiply layers and other modes only to surfaces. But it's not the only way. If you rather aim for a style where the original line art is not visible, you can still start with the Multiply layer. You then move to a Normal-mode layer and re-paint the lines yourself (such as making the curve of Red Sonja's hip a yellow line instead of black). This can look very impressive but is a very different style and also very labour-intensive. Once can of course also try a hybrid of the two.

So what you're suggesting is that I color the entire image roughly, with whatever colors I want to use. Then work on a "Multiply layer" to get the other tones, shadows and highlighting colors?

Couldn't I in addition use the, "Gimp Lighting Effect" to Improve the lighting condition?

What about using a 3D program, such as "Blender" to adjust the lightning of the rough color draft?

@Wallace

No, colour everything on a Multiply mode layer. Only one such layer is needed, really. This will preseve the lineart and allow you to experiment. In principle you only need other layer modes for very specific highlights or colour shades.

I don't use many GIMP filter effects, so I cannot comment much on those beyond the fact that they are not needed to get good lighting. Their result rather tends to clash with brush work in my experience.
I would not use Blender for a 2D painting like this. It would be interesting to see it tried but it's hardly necessary: If you want homogeneous lights, use GIMP's gradients instead.
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Griatch

I understand and thanks for this explanation.
I've done coloring in the bast and have never attempted to do it this way.
It does seem like a natural means of trying to create/mimic lighting where there is none.

This is going to be a project that I giving much attention to, and I want my end results to be as perfect/stellar as possible.

This topic has been excellent! Very instructive! Thanks to Wallace and everyone who gave their opinions!
Thanks to jam4ck for the script - translate into palette, very interesting! - Although too buggy and unstable closed my gimp sometimes :-(

Thanks Akros and I agree.
I just hope to be able to take away from this post what I can, to help me in creating a "masterpiece" of coloring. Or at least a very well colored image.

I ended up making a flesh gradient and then "mapping" the gradient to a grayscale coloring of Conan's skin.

The image on the left is the old skin coloring of Conan, that I didn't like so much. The image on the right is the one I did the "Gradient Map" to. I think it came out much better then the old version, so I'm going with this version.
I'm not crazy about how I did Conan's hair. I find hair very difficult to color, especially "black or white hair".

What do you guys think?
Also, would anybody have any tips for coloring "black hair"?

Don't make it black. Hair has shine and is affected by the colour of the light in the room. Highlight it with the colour of the light sources hitting it. Which means you have to start with the light sources ...

... But then we are back to what I recommended twice now - to paint the whole image rather than focusing on one detail at a time. Spending any effort on the hair (or on any other minute detail) at this early point is just a waste of time - you can't know what colour they should have until you have roughed out the entire image with lighting and hues.
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Griatch

Thanks Griatch, you do know better then I about such things. I do understand what you're saying, but I don't think I'm going to take that approach. I'm actually not sure what I'm going to do at this point.
As it stands, the coloring of this drawing is on hold.

when I color black I make it blue do all my shading then make to copies of the color, one blue and another I make almost black then I overlay the blue one to make it look more interesting.

Thanks Mokonafan, that sounds like it just might work.

I really like that lion coloring, very detailed and dramatic.

My recommendation has not changed in 2.5 years, but since you want to do every piece individually and not rough it all out first, you need to be very careful so the different components fit together in the end.
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Griatch

Well no-one can accuse you of lacking in stick-ability Wallace.
Looks good to me but good job you're not being paid by the hour!