On the topic of RD's perceived gender... I have to join the group of those who instantly classed her as male and became wildly confused when every pony referred to her as "her". This was before I'd realized the visual differences between male and female ponies, so it was all based on the voice.

I've come to accept that RD is a girl and it's all fine, but even though I know better, occasionally her voice still throws me off a little.

However, to me, Zecora is much worse. Even to this day I can't hear that voice and accept that she's supposed to be a female. Every time the ponies refer to her as "her", my brain shuts down a little. It isn't helped by the fact that Zecora actually looks rather like a male pony too, with that squarish snout.