I can't seem to write §3 in any text entry field (e.g. signs, or anvils). Using the right code in other applications works perfectly, but not in Minecraft. This happens both on Mac and Windows. I've tried copying and pasting from another text field in another app, but that doesn't work either. The rest of the text copies, but not the code. This includes any color code specified after §.

E.g. using "This is §3 a test" yields "This is  a test" in Minecraft, without any color formatting.