Final answer:
The colour of an indicator for real estate authorization is not a standard practice and typically, authorization is confirmed by licenses, not lights. There is no accurate answer without further context.
Step-by-step explanation:
The colour of the indicator light that signifies whether Sam is authorized to trade in real estate is not established by any standard system and is not typically associated with the field of real estate trading regulations. Such a system seems hypothetical and is not part of real-world real estate or legal practice. Real estate authorization is usually confirmed through licenses issued by government agencies or professional regulatory bodies, which can be publicly verified. Therefore, without additional context specifying a unique system where colours indicate authorization status, it's not possible to accurately answer the question.