I know it must have something to do with fonts but if you look at this question in the iOS app, the diamond ♦ is red.
On every other system the diamond shows up the same color as the rest of the words.
Why is that?
Fixed! This came up in some other new features we're working on, so we just fixed it. We're doing things client-side on fields which could contain diamonds they may still pop up some places (file a bug report), but questions are fixed all over the place. The secret sauce is some sweet sweet regular expressions:
Pattern: [\u2666](?=[^\uFE0F\uFE0F]|\z) Template: $0\uFE0E
Note that I am not removing the Unicode variant if it exists. I am assuming that if you inserted a big red diamond in the editor, you want a big red diamond in your post.
Old answer (aka why is this happening to me?)
So... I looked into this and it appears that iOS is performing a legitimate Unicode 6.1 rendering of that character. Diamond characters
U+2666 have two standard variants:
2666 FE0E ♦ BLACK DIAMOND SUIT text style 2666 FE0F ♦️ BLACK DIAMOND SUIT emoji style
When you don't specify what variant to use, the renderer gets to pick. WebKit, probably trying to be consistent with the rest of the universe picks FE0E, and UILabel/TextKit/CoreText, trying to be hip with the younger crowd picks FE0F.
When it comes to emoji, I don't know why they picked boring old
U+0039 U+FE0E when
U+0039 U+FE0F is available. Just my personal opinion.
That's because the diamond character that is used happens to have a corresponding emoji, which is rendered differently from all other glyphs in certain views on iOS. It's the diamond suit character; each other playing card suit has its own emoji as well.
Sent from my iPhone
It's red in the Android app too. It's even a playing card!
I think diamonds have been styled to draw attention to them when they could be a fairly small and hard to discern symbol on the phone. I'm not sure if that's the exact reason, though.