#TheShoe Mystery Solved -- The Right Answer Is ... It's Complicated

There's a really good reason to argue about that pink/purple shoe thing that's been trending -- because a giant optical illusion without any clear answer. Aaaaargghhhh ... said the Internet!!

We talked to Ava Munro, the woman who posted the pic, which reminded people of #TheDress, from earlier this year.

Munro's intention was to solicit advice about what to wear to a gala -- but instead she sparked debate about which nail polish MATCHED the shoe.

The truth is, neither does. The nail polishes -- made by Sinful Colors -- are both shades of purple ... Dream On #113 and #50.

Meanwhile, the freakin' shoes are ... MAGENTA!!! For the record, Munro says the shoes more closely match the nail polish on the right. But it's not exact.