I really ought to just bite the bullet and go read some color theory stuff - if they taught me any at school I forgot it.
I know I'm a bit of a noob on this forum (first post!) but I know a little bit about color theory. Here's the basics:
The color wheel. You can find these anywhere. Just make sure that thet correspond to the paint spectrum rather than the light spectrum (most computers use the light spectrum). The color wheel is the basis for all color theory. How you use it:
-First of all, the types of colors (this you probably know). The three colors red, yellow, and blue are the primary colors of the paint spectrum. With these, you can mix any other colors. Mix them all together and you get brown. When you only mix two, you get the secondary colors green, orange, and purple. Mix a secondary and a primary and you get the tertiary, or intermediate, colors.
-colors that are across from each other (i.e., red and green, purple and yellow, etc.) will often make each other stand out much more. Say, for instance, that you're painting a goblin (not relating to anything in Berserk). You decide to give the goblin green skin. By painting his eyes red, the color directly opposite green, and by using greenish or colors with low saturation, the red eyes will stand out a lot. These are called complememntary colors. Don't overdo it though, a picture that's about half pure green and half pure red will look like it stepped out of christmas.
-This rule can also be used by applying colors which form a triangle on the color wheel, such as all the primary or all the secondary. Aparently this works for colors that form a square too, but that stuff's really advanced.
-Colors that are next to each other on the color wheel are called...something else that I can't remember. Using this can work quite well if done correctly. For example, Proj2501 used pretty much only red, orange, and purple in the pic he posted here. The emphasis on the red helps depict the agression. This technique is usually used to invoke a particular mood.
-Another thing to note:there are basically two categories of colors: warm and cold. Warm colors are reds, yellows, and oranges while cool colors are blues, purples, and greens. This is again is mostly used to invoke an emotion. You wouldn't want to use blue to depict a scene of a warm and loving family.
-Basic Jargon: Hue reffers to a color. Saturation refers to how much black or white (which are considdered tints and shades, not colors) is mixed into the color. Lithrael, for instance, uses mostly colors with a low saturation, which gives the pictures a very fairy-tale-esque look, in this case a very good thing. Try not to vary the saturation too much though, or the picture won't look very uniform. Acromatic reffers to a composition without color (i.e., the black and white illustrations straight out of the comic) and dichromatic reffers a two color composition.
That's about it, hope I didn't write too much. And complements to your work, you're an awsome artist (I'm know a bit of theory, but my work can't compare.).