Bit of a confusing one, the color attribute is respected on the desktop version of Safari but not on mobile.
I tested it on an iPhone 5 (iOS version 9.2.1).
Sample code (first span will appear black on safari mobile):
<html>
<head>
<style>
span { color: white; }
</style>
</head>
<body>
<span>✖</span>
<span>×</span>
<span>×</span>
</body>
</html>
and JSFiddle link: https://jsfiddle.net/9t3v8846/
Adding !important didn't do anything. Any ideas what might be causing this?