What color is the air conditioning compressor clutch relay on a 1994 jaguar XJ6?

There's no standard color for a relay, including the A/C compressor clutch relay, across all car makes and models, let alone across the years of production for a single model like the 1994 Jaguar XJ6. The color is determined by the manufacturer of the relay itself, not by Jaguar. You'll need to consult your car's wiring diagram or a repair manual to identify the relay. Look for the relay associated with the A/C compressor. The diagram will likely show its location in the fuse box and may indicate a part number that you can then use to identify it.