My own scribble testing results in an unequivocal yes. The paper is noticeably different, using the various writing instruments shown above, plus a few others I tossed into the mix after the initial results. And to tell you the truth, even knowing what to expect, I was surprised that I could detect the difference so easily.
All the pencils were far quieter on the white pad, and noticeably louder on the yellow. This was especially pronounced in the mechanical pencil, which maintains a very narrow tip, but even that big chunky Moleskine pencil was markedly different. The yellow paper absolutely gives more feedback as you're writing on it. The white pad is nearly ninja-silent with a pencil.
Almost all of the pens I tried with a "fine" or "medium" nib exhibited the same properties: more feedback, a touch more noise. My red Sheaffer school pen is notoriously scratchy on cheap paper, and I tend to use it only on nicer paper as a result. It magnified the difference in surfaces between the two pads, though it wasn't unpleasant on either. Most medium-nib pens were noticeable. Only when I moved up to the italic-nibbed Pilot did the differences go away. Perhaps the wideness of the nib skates over the tiny surface differences, or I'm just not a good enough penman to know the difference.
Given this result, I brought out a couple more extreme examples: a super-fine rollerball pen, a couple of colored pencils, a cheap ballpoint, and a broad calligraphy nib in a plastic Sheaffer, cousin to the school pen. All except the calligraphy pen were different. What's more, the Calligraphy pen revealed tiny amounts of feathering on the yellow pad, and even a few pinpoints of ink bleeding through. Were I a calligrapher and not just some slob, the yellow paper would be demoted to the "practice only" pile.
The last thing I've tested out is front-versus-back. Paper has a finishing step when it's made, and I remember from a few mis-spent summers as an all-around-office-boy that there's a "right" and a "wrong" side to paper. Wikipedia has a piece on paper sizing if you want to know more -- sizing as in finishing, not on paper sizes, which is a different article. The final round of tests was comparing writing on the front and back. I'm less sure about this test: sometimes I'd swear that the back of the white paper was rougher than the front of the yellow, at other times there were about the same. If there is a quality difference between front and back, it's a tough one to discern.
Three final observations to make, and then scans of the front-side tests are after the break.
First, the white paper is cooler to the touch, as in temperature-cool, not leather-jacket-and-Harley cool. I'm positioned underneath an air vent which can't help, but by resting a hand on each, the yellow paper warms up faster. Color difference? Surface difference? The magic of thermodynamics is at play, anyhow. There's a thesis in there for a physics student, perhaps.
Second, the yellow paper just seems thinner. I don't have any reason to doubt the stated weight on the cover, and have no way to verify it beyond just a shake test, and noticing things like ink bleed-through and show-through. For an extreme test, I have a disposable fountain pen filled from one of those inkjet printer refill kits which practically pours ink down the nib. The resulting letters show through on the yellow, less so on the white, though neither are very happy with trying to hold that much ink. I didn't say it was a fair test.
Third, and finally: although the yellow may have come out "worse" here, it's the better of the two in certain circumstances. If I were a student and using pencils on a regular basis, the white paper is quieter and smoother, but the yellow is surely easy on the eyes after a weekend binge or an unfortunate move to Daylight Savings (or both.) Some of the pens find the white paper almost too smooth. The Pelikan, for instance, always wants to skip on the white, but is fine on the yellow where the surface of the paper and the capillary action of the nib mumble mumble mumble handwave it just worked better, OK? This is not an unusual circumstance for pen owners, as we're always looking for
So, there you go, Exaclair -- a highly unscientific and unfocused confirmation of your own customer feedback.
When my daughter and I get the chance, we're going to kick off our own more involved tests at home, comparing to other brands of yellow and white writing pads. Stay tuned for that, and a return to rhino-and-roo, the paper pals.
Writing sample scans. Please excuse the inanity of the text. Click to embiggen.