Why did my strawberry cookies turn blue??

I had an idea to bake strawberry cookies dyed pink by nothing other than the natural juices of the berries.  All but a few of the recipes I found online use food coloring or jello mixes.  So I took bits and pieces from a strawberry cookie recipe and a strawberry cake recipe (both recipe designers had achieved pinkness without the use of artificial coloring) and blended the strawberry parts with my favorite butter cookie recipe.  At first I thought I too had achieved success.  The cookies had a slightly unappetizing tint of gray but were mostly pink.  To my dismay, less than 1 hour after I had placed the cookies on the rack to cool the entire batch had turned blue.  My patchwork recipe was an epic fail!  Why did my strawberry cookies turn blue??  With some more experimentation I may bake a perfectly pink batch, but for now I think I’ll focus on my next project – fresh blueberry cookies.

Recipe #1: Blue Strawberry-Flavored Cookies

Slice 1 cup of fresh strawberries.  Sprinkle strawberries with 1 tsp of granulated sugar and let drain in strainer over a bowl for 1 hour.  Save the juice.*

Blend strawberries with 1 tbsp lemon juice and 1 1/2 tsp vanilla until smooth.

Combine strawberry mixture with 1/2 cup butter (1 stick), softened, and 1 cup packed brown sugar.  Mix well.

Add 1 egg. Mix well.

Add dry ingredients: 2 1/2 cups flour, 1 tsp baking soda.

Then add 1/2 cup white chocolate chips.

Bake at 375 degrees for 4-5 minutes.

*I later used the leftover strawberry juice as flavoring for a basic butter cream frosting (powder sugar and butter). So simple, but so good and a tasty addition to these cookies.