Hi Max,
That enlarging window is a fallback when the user is trying to EyeX-click something too small or something that cannot be recognized as an EyeX interactor. If your application is using the EyeX SDK to register interactors, this window should not show up.
It is not possible to change the color of this circle as a user of the system, but I have forwarded the feedback about poor visibility to the responsible UX engineer.