I haven't heard the special red 535, but the se535 compared to the 4R is an interesting comparison. I find the westone is smoother from top to bottom in terms of frequencies. I wouldn't call either of them flat or neutral, but if I had to choose I'd say the 4r is more flat sounding by default, but also more dull sounding. The 535 is more vibrant sounding, but ironically dull in it's own way due to the treble roll off.
The 535 is still more interesting sounding by default though, but the highs ruin it for more in comparison to the 4r. They beat lesser phones though in overall quality. With no modification the 535 bass is beefier a bit than the 4r with more warm body. The 4r has more smooth bass transition, but it is lower in level and more masked in the mid bass.
I don't like giving impressions on something I haven't heard, but if the red 535 really bought the treble up a lot on the high end, more like high treble, I think they might beat out the 4r at least in terms of enjoyment for me personally, but I think it would have to be substantial. The high treble would need to be almost four times what it is or something like that. A small boost in high treble still probably wouldn't cut it for me. If it is a significant boost that's another story. Then I would still call the 4r smoother overall, but less vibrant, energetic and musical.
Unfortunately, I'm always looking for neutrality. In this case, neither of them are really that neutral in the truest sense of the word. If you bring eq into the equation I think the 4R handles that better. The 4r can be brought to sound extremely neutral with eq. Again, I can't speak for the red 535, but the standard se535 just didn't match the same level of neutrality with eq that i am able to achieve with the 4r. I think this is partly due to the fact that the 4r by default reproduces more frequencies overall, so it has less to make up for. It is also smoother overall, so eq adjustments make better results. Finally, eq aside, there is nothing you can "eq" to change certain aspects of each of their sounds, and in that case the 4r sounds more "true" to sound to my ears. Again, this is EQ'd though. Without eq the 535 "would" be better with a substantial high treble increase. Otherwise, I prefer the 4r, even without eq.
Not sure if that helps. Maybe someone can post graphs and in depth details about the difference between treble in the two 535 models?