Here's a small tutorial on how to paint Dark Eldar. The theory behind it is that the DE use different shades black that only really reflect color on the edges. As such, we'll only be putting color on the edges.
First step after assembly and priming is to mix VGC Chaos Black with water in a 1:1 ratio, then apply this over all the areas that will be predominantly black, such as the armored carapace. This is done because primer black tends to less vibrant than the paint-on acrylic black and Chaos Black will help the model's overall tone and aid in blending.
Next you'll block out all of the metal areas in GW Boltgun Metal, after the areas are thoroughly dry you'll wash with GW Badab Black. Clean up any areas where you strayed onto the black areas with VGC Chaos Black.
Our next step is to thin out some GW Necron Abyss, just enough to help it flow. We'll then take the color and rim the edges of all the carapace. Remember, two thin coats are ALWAYS better than one thick coat, especially for this style of painting. One of the reasons why this style is easier than most for blending is because you keep your paint thin, using the paint's translucency and allowing the previous layer to show through, enhancing the color progression and blending. The width of the line you put on the edge of the carapace depends on how vibrant you want the overall effect to be. If you want your carapace to look like a dark depthless black with the faintest of color, use thin lines. If you want the color to be more apparent, use thicker lines.
Next up is VGC Imperial Blue. Use the same method and go over the same areas. Because we already have the Necron Abyss base coat down, this step should go quicker and you should have less areas where you'll need to go back over twice.
The last two steps require more discretion. We'll be edging again with VGC Magic Blue, but you'll want to keep it VERY thin, remembering to allow the previous layer to show through. Here you'll have to decide which areas to highlight. On mine, I chose to highlight the "upper" areas, as if the light source for the highlights were directly above the model. take a close look at the pictures and you'll see what I mean. You have to imagine how light would reflect off the surface of the model.
The final step is done with VGC Ice Blue. This will be done very sparingly and only on the corners.
So, that's the hard part done! As long as you've got a good color progression, you can use this technique for almost any color. Here are a few recipes for those of you who don't want to do just blue:
VMC Burnt Cadmium Red
VMC Burnt Cadmium Red + VMC Carmine Red (1:1)
VMC Carmine Red
VGC Bloody Red
VGC Bloody Red + VGC Fiery Orange (2:1)
GW Orkhide Shade
VGC Scurvy Green
VGC Jade Green
VGC Foul Green
VGC Chaos Black + VGC Liche Purple (1:2)
VGC Liche Purple
VGC Warlock Purple
VGC Warlock + VGC Tentacle Pink (1:1)
VGC Scorched Brown
VGC Scorched Brown + VGC Dark Flesh (1:1)
VGC Dark Flesh
VGC Dark Flesh + VGC Bleached Bone (2:1)
VMC German Grey
GW Adeptus Battlegrey
VGC Cold Grey
VGC Stonewall Grey