For those not familiar, on an iPhone the green background only occurs on the messages the iPhone user has previously sent, and not those they have received from others. Also, whilst they’re typing, they do not have a green background in the text box. However, that said, to my eyes, the green background does indeed make it slightly harder to read what you’ve previously sent compared to the blue backgrounds of iMessage, or the black on light gray of received messages. But it’s slightly less of a problem to me because I generally remember what I’ve typed well enough to give my eyes an advantage.