What Are The Ingredients In Sunscreen That Make Skin Purple?

What ingredients in sunscreens make my skin purple. I am dark skinned not really allergic to anything i know of and almost all the sunscreens i try above SPF 15 have that affect. I would like to use a higher SPF because i am a lifeguard in the sun a lot. Everyone thinks it is a joke to slap a purple hand print on my back and laugh. Its doesn't bother me in any way other that looking purple.