TBH, my main problem with the C-bag shower cap isn't the colour[1], so much as the way that it impairs access to those ever so useful rear pockets, and if not fitted carefully (eg. when thrown on in a hurry as it starts to piss it down with rain) it can obscure the front light.
[1] Theoretically, it shouldn't be a problem, as dorky hi-vis is automatically cancelled out by application of Rule 9 in situations that warrant its use. In practice, as I've mentioned above, you have to put it on *before* it chucks it down for it to be effective.