/setblock ~ ~ ~ standing_sign 0 replace {Text2:"{\"text\":\"\u00a72Green\u00a7r\"}"}

will not work because \u isn't escaped properly. This can't be a works as intended, as it works in 1.11.2 (if it is, you guys should seriously consider re-adding it). The result is supposed to show green text using a section sign (I do know how to use JSON text in a sign, it is a long story why I need a section sign specifically), but returns an error as the \u isn't escaped properly.