1955 opc cards? Gray back
 

Is there such a thing?

Series 1 (1-89, 100-110) come with two back types. I called them white and cream in my checklist since it’s not really a grey stock. This looks like one of those darker variety backs to me.

Grey
 

This is grey stock
Here's all 3

It looks like the darker cream from here, not grey (like a 1957 Topps card). But pictures aren’t always accurate. Very cool find if it’s on grey stock

Definitely grey stock