The odd one out is white.
The other four colors, violet, blue, green, and yellow, are all primary or secondary colors. Primary colors are colors that cannot be created by mixing other colors together. Secondary colors are colors that can be created by mixing two primary colors together.
White is not a primary or secondary color. It is a tertiary color, which is a color that can be created by mixing a primary color with a secondary color. In the case of white, it is created by mixing blue and yellow.
Therefore, white is the odd one out in the given set of colors.