Thanks! If you have a calculations workflow already, what would the contrast ratios (even if approximate) be for old iOS? To a human eye it truly looks like SMS got way worse whereas iMessage stayed around the same.
The pre-iOS 7 graphics have black text over a non-uniform background color as compared to white text over a uniform background color. This gives us ranges instead of a single value, but even in the worst case, black is a vastly more legible foreground color:
