Indeed!
The fact that Grado goes to the trouble of matching transducer pairs with each other points out this variation quite prominently, I think.
Also, I once read about an experiment where people were listening to the exact same speakers for each listening session. Not just the same make and model, but the exact same speakers in the exact same room with the exact same upstream chain and source material. The only thing that changed was the color of the cloth covering the speaker grilles! And yet, across all genders and age groups, there was a significant difference in the perceived sound, especially with certain colors. And, black didn't fare that well, actually! IIRC it came across as cold and thin. Blue and red did better. Yellow was harsh. Etc. Anyway, point is that it really is crazy what kind of subjective stuff can happen in this realm. And in this case, maybe the brown and beige vs. the black color is having an effect! (Maybe! Or maybe not, since you can't see the cans when you're wearing them.)
And yet, despite stuff like this, we all make comparisons against cans we've heard before but not longer own, or never owned, etc. I do it. It seems necessary. It feels reasonable. I made a bunch of comparisons between the Grado RS2e's and the SR225e's, despite the fact that I had only auditioned the 225's in a Stereo store for 2 hours a week before.
And I still think there was something objectively true in this. Certain parts of certain songs were physically painful on the 225's (upper treble) which didn't stand out much at all on the 2e's, and so on. That seems to be more than just subjective. But then, on some days our ears and hearing is different than on others, depending on how much sleep we got, whether we are hungry or not, stressed or not, happy or not, etc. So who knows!
In any case, I will be interested to see if a consensus develops here in regards to SE vs. beige. Unfortunately, I only own the 595's, so my comparison will be between that and the 598SE's.