This evening I was updating a website for a customer and noticed on my iPad and iPhone that Tel: +31 (0)123 456 789 numbers got a different color instead of the color i submitted in the CSS code.
As i didnt do any CSS on the element i started searching and found out you can prevent this by adding a metatag:
<meta name="format-detection" content="telephone=no">
This should prevent mobile browsers to mark telephone numbers as blue / hyperlinks.