Here's a link to PSA's population report for the 1956 Topps baseball cards. The white backs outnumber the gray backs from 1-100 by a better than two-to-one margin. From 101-180, the white backs appear to be quite scarce compared to the gray backs.
Only one dated team card shows a gray back. The Cleveland Indians show a single example, graded a 4.
https://www.psacard.com/pop/baseball...56/topps/49737