I have an issue about 'Color Contrast Calculator' tool in Accessibility Inspector from Xcode.
For same foreground color "#067AB4" and background color "#F5F5F5", the color contrast ratio calculated by 'Color Contrast Calculator' is 5.5: 1, but is 4.3:1 by other tools like 'Colour Contrast Analyser' or https://webaim.org/resources/contrastchecker/
So with the same foreground and background color, why the color contrast ratio is difference with other tools?
Because web access via a computer and it's attached display, are different from an iOS device's display and rendered c/c ratios thereof?
Are you sure there is a standard definition of constrast, or stated otherwise, that the different tools use the same definition. It is an open question, I just don't know !
Edited
Found this,
h ttps://en.wikipedia.org/wiki/Module:Color_contrast
which seems or pretend to be the mathematical definition of contrast between 2 colors.
Let you play with. Thanks to tell if you find something interesting.