control
These colors were present in Android framework before Android U, and used by MDC controls. They should be avoided, if possible. It's unclear if they're used on multiple backgrounds, and if they are, they can't be adjusted for contrast.* For now, they will be set with no background, and those won't adjust for contrast, avoiding issues.
* For example, if the same color is on a white background _and_ black background, there's no way to increase contrast with either without losing contrast with the other.