May be normal cycling.

See this: Strawberries in the homegarden
http://ucanr.org/sites/gardenweb/Berries/Strawberries/

Here is a link that might be useful: Strawberry info from UC

Don't know for sure but, the numerous, small dead spots remind me of damage from piercing sucking insects. The purplish coloration may be P deficiency, do the affected leaves' undersides show the purple worse and more so along the veins?

Just brown