Childrens Book - Boy purple spots on face?

Childrens fictional book from early/mid 90s or before
I believe the cover photo was of a boy squinting his eyes shut with purple spots on his face
I believe the story was about a boy that was sick or had chickenpox or something with bug juice

Probably Freckle Juice by Judy Blume.

Yes! That is exactly it! Ahhh, I knew I was basically giving nothing to go on and it's been killing me. Thank you so much!