"Mitigating circumstances" should accompany a guilty plea. They are not needed in the event of a not guilty plea.
Bearing in mind that before the red light was displayed, amber (which also means "stop") would have been displayed for around three seconds, what circumstances would you suggest might lessen the seriousness of that offence?.
You (assuming it is you) may be offered a course or fixed penalty for the offence. If you want to accept either of them, you must accept the allegation as it stands. Only if your case goes to court will any mitigation be considered.
