Blue Shift

"Blue shift" is a term used by artist. Blue shift is a problem that can arise when we shoot white over another color. Now if we shoot solid white against a darker color it will not be a problem. Where the problem can arise is when we blend (fog) white over another color. let's say we are doing some shading from red to white on the side of a fuselage. In other-words it starts out as solid red and turns into solid white. In this case if we start with a white base and then blend red back over the white we won't have an issue.

But let's do it the other way around. Let's say we shoot the red first and then start blending (shooting) white over the red to create the same blend. What can now happen is where the white is transitioning to the red, we can get a really ugly shift in the white towards blue. At the extreme, the white in those transition areas can turn to a muddy gray.

Here is the theory. If we just take a dot of white and put it over a red base and look very closely we may see a little bit of blue at the edges of the white. Now if we were painting a picture with oil paints it may not be an issue, but let's think about what happens when we use an air gun or airbrush. What happens in an airbrush or gun is the paint is broken into thousands of little tiny drops. So if we think about a blue halo around each one of those little dots, we can see how blue shift can occur.

The bottom line is the way to prevent it is to shoot the dark color over white, not the other way around. Airbrush artist sometimes mix a drop or two of orange into their paint to counteract it from happening. Remember Orange is on the opposite side of Blue on the color wheel.