I didn't read the cupcake fanfict but I think I have known enough about that. I promise there is no much implication in this picture.
"what's the red stains for?"
"They are from the paint needed to paint the apples cherry red so they can pretend as cherries." said Pinkie"What else can it be,silly?"
The thinking proccess actually was: thought a cheery should be added=> normal cherry too small=> can use an apple to replace=> apples and cherries are not alike=> paint the apple cherry red=> cherry red paint everywhere
but after I drew, I found the colour difference was not that great but I had already drawn the paint and could not bear to remove it. Silly me.