The problem with the wrong coolant is not that it won't cool the engine sufficiently (plain water will happily do that), but that it will cause corrosion in the engine, cooling system, or both. I would recommend putting the correct coolant in with as thorough of a flush as you can.
Also note that the color of the coolant is typically a decent indication of its compatibility, but not an absolute one. Make sure to use coolant that is compatible with the engine (sadly coolants don't use type certification/specification like oils (engine, transmission, etc.), so it's hard to recommend anything specific other than "go to the manufacturer website and check compatibility with your car").
My owner manual (2018 BRZ) just says:
Quote:
* SUBARU Super Coolant
* Similar high-quality ethylene glycol-based non-silicate, non-amine, non-nitrite, and non-borate coolant with long-life hybrid organic acid technology
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