The latter article doesn't cite decreasing contrast ratios, but notes
[Apple's] guidelines state that you should strive for a minimum contrast ratio of 4.5:1 between the text and background colors. Apple’s white text in a blue bubble (iPhone messages) shows a 3.5:1 contrast ratio, while the white text in a green bubble (non-iPhone messages) manages only a 2.1:1 contrast ratio, less than half the recommended minimum contrast