I was going to make the same point, both about colour (or any visual indicator) not being the only distinguishing factor and about tactile indicators being a helpful way to distinguish things. I’m legally blind, so I actually depend on tactile more than visual. I find pens of different brands easy to tell apart actually. But pens of the same brands are identical (with the exception of Sanofi, who do include tactile markers on their reusable pens).
Ideally, pens in the same brand would have both obvious visual and tactile features that distinguish them. But I think pens of different brands may be more difficult since the companies probably aren’t communicating during product design.
It’s not braille, but the Sanofi reusable pens have good tactile markings on the end of the plunger to differentiate the blue and silver pens. But they are the only pens with tactile markings I’ve come across. The NovoPens I’m using now are totally identical except for colour (and the fact that one pen doses half units and the other pen doses whole units).