I'm sorry but technically it's not possible. Forest uses two methods to support the render engines:
a) If the engine provides a SDK, we write the implementation (VRay, Mental Ray and Maxwell Render).
b) In other cases (VRay-RT, Arion Render, Octane, Thea Render and Corona Render), we provide an interface to their developers, so they can read the Forest items and instanciate them (simple scattering).
Forest Color requires to write a custom material shader, so it's supported only if the SDK is available and it allows this type of shaders (currently VRay and Mental Ray).