Found: YA boy only one to realize painting replaced by fake

FOUND: This was a favorite book when I was a teenager in the early 70s in Texas. A boy sees a painting on loan to a museum and is deeply affected by it. He goes frequently to view it, then one day he no longer gets the feels. He realizes it's a fake but nobody will listen to him so he has to investigate himself.

I seem to remember something about an eye on the title or on the cover. Not sure, might be a red herring. I believe the cover was mostly red. It was pretty short, maybe 100-150 pages.

When I try to remember the title "Something Wicked This Way Comes" pops into my head so I wonder if there is some similar phrase in the real title.

Deathman, Do Not Follow Me by Jay Bennett?

That's it!! Thank you so much!