It's been explained before that colors are used to assist the camera crews in following the teams during the Race, especially in situations where teams are in a group, or a team is in the midst of a group of locals, such as public transit or a crowded street.
How this is done is not as clear (or at least I've not heard of how), but it does seem as if teams give input (choosing a color) and bring clothing having that color, or teams are told before they depart for pre-start sequester the color that is being used for that team so they can bring clothing with that color.
The one thing that is clear is that there's no coincidence involved.