Leaks of any kind are always a pain to diagnose. The best you can do is degrease the area well and then check back when you notice the leak and try to trace it to its origin.
It is difficult to tell on color alone, as it travels it gets contaminated with other residual fluids and by the time it makes it to the floor it could contain oil, diesel tranny fluid and coolant all in one, so the only way to know for sure is cleaning well the entire area. You may also want to try leak detectors if visually you cannot find the source.

Good luck

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Stable Mates:
1987 300TD 310K mi (Hans)
2008 Jeep Grand Cherokee OM642 165k mi (Benzrokee)