For a while now I've been itching to use my airbrush, and since my Tau were in need of some additional transport, the Devilfish naturally presented itself. I wanted to try a technique that would result in an optical illusion. The intent was for the vehicle to have camouflage stripes across the hull--these stripes would be of a single color, but the color would appear to change from one shade to a different shade depending on what part of the model you were looking at. The way to achieve this is by shading the hull itself--the backdrop to the camouflage stripes--in shades of color that are darker or lighter than the shade of the stripes themselves. Just what this means will hopefully become clear as I explain it.
Step one was to assemble and prime the model.
Next I used the airbrush to basecoat the model Jade Green. Unfortunately Games Workshop doesn't make this color anymore (all the more frustrating because it's a primary color of my Tau army), but fortunately Vallejo Paints does, and it's a perfect match.
The Jade Green would become the color of the camouflage stripes. I took some blue painters tape, laid out some strips of it on a cutting board, and using an exacto knife and a ruler, cut out strips several inches long and 1.5-2mm wide. I then carefully put the tape on the model where I wanted the stripes to be. The narrow width of the tape allowed me to curve the tape over the model's edges and also to make wavy lines without the tape wrinkling. I know that the blue tape doesn't show up well against the jade green of the hull, but if you look closely, it's there.
The next step is where the optical illusion begins. I used my airbrush to paint Scaly Green (another color Games Workshop is unfortunately phasing out) over the rear half of the model. I did full coverage of the rearmost parts of the model, and moving forward along the hull, I used progressively less paint, fading it out until across the center of the model (roughly where the side doors are), I gave it the barest dusting of paint. The next step was to paint the front half of the model Vile Green (again, Games Workshop doesn't make this color anymore, but Vallejo Paints makes an identical shade: Foul Green). This time, I painted the Vile/Foul Green over the front parts of the model, completely on the foremost parts, and fading it out as I moved backwards along the hull. When I reached the midsection, I faded it out completely. The result here was to make the model look Vile/Foul Green on the front, blending gradually into the underlying Jade Green in the middle, and then blending gradually into Scaly Green in the rear.
The next step is to remove the masking tape. In some places the tape wasn't easy to remove, so I had a use an exacto knife to get it started, being careful not to scratch any of the paint off. If there was some bleed through of the airbrushed paint onto the camouflage stripes, I touched it up with some more Jade Green.
Finally I put on some black trim and other details, put on the drones, and applied a couple decals. I also attempted to use the airbrush to paint on some soot lines by the engines using black, but the result didn't come out as "sharp" as I was hoping--next time I need to use a finer airbrush nozzle. So here's the final result. Hopefully you can see the optical illusion: the camouflage stripes look dark against the front of the hull, but lighter colored on the rear of the hull--but regardless of where they are on the model, it's all Jade Green. On the midsection of the model, the color actually fades away into the background for a little bit before reappearing on each side as contrasting again with the background.