Apple is not going to change this unless legally forced to because it is quite possibly the biggest driver of iPhone sales.
A whopping 87% of American teens use an iPhone, and the green text from Android SMS is the biggest reason. At that age people will do almost anything to fit in and get a date, and the green text was chosen specifically to elicit an "eww" response. Most of those teens will likely will continue to use iPhones as adults because it's what they know.