If you're using the correct spec ATF for the 722.6, it does turn a darker color although mine generally still showed some pink when dripped on a paper towel.
I would just change it out and make sure to measure it at the same temperature. It should be filled to the high mark when hot.

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Prost!

That is the plan. Fluid is definitely pink on the paper towel. But seriously darker than the fluid in my stock 560SL with the 722.3 Transmission which has also been drag raced. I may just not be used to these 722.6 transmissions. Maybe that's why they were sealed for life, MB didn't want anyone to see the transmission fluid color.

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John Roncallo

As the friction material wears, it ends up staying in suspension in the fluid making the color dark. It isn't getting dark due to it overheating.

I've pulled apart a few .6 trans that were in the 164 K mile range , had original filter ( date code was prior to build date ) and the amount of material in the pan was near zero. You would have thought the trans has 30 K miles based on what was in the pan.