That is in fact one of the accessibility settings. Increases contrast front the blue bubbles too, and color contrast between foreground and background colors system wide.
This might sound strange but most people with iPhones actually like how their phones look and behave. Personally I’m not the biggest fan of this era of UI design, but it’s silly to assume hostility on Apple’s part. Every year they announce even more accessibility features, and it makes sense to because they really want more people to actually be able to use the phones they sell.