The colors themselves are not representative or relevant to the actual styles in any way. They are design and branding choices that differentiate Everything DiSC from other assessments.
Inscape (now Wiley) was the first to use the circumplex model and they chose colors to visually differentiate the styles. They show how someone has aspects of each style. It's obvious through the color shading that someone with a iC-style also has a little bit of D, i, and S.