Summary
IOS sets the text color of buttons in the useragent stylesheet to blue. No other browser does this, and it should follow suit. Normalize.css should set the button to inherit the color from it's parent by default, similar to how other properties are done ie. font-family. I've added a screenshots to show that in our case, we're setting the base color to black, and then IOS safari is actually overriding that.

Task
Add color: inherit to the button tag to override the useragent styles applied by IOS