What you see is what you get has an interesting provenance, starting with technology, moving into stand-up comedy, then back to its techno roots.
The phrase pops up for the first time in connection with color photography, where what you see really is what you get. It’s FirstMention dates to a May 2, 1936 ad in the Chicago Daily Tribune.
Can you see it there? Just in case, here it is again.
The phrase shows up occasionally in its own on-and-off fashion for a few decades until comedian Flip “the-debbil-made-me-do-it” Wilson grabbed hold of it for his comedy routines on his national show in 1970. His character, Geraldine, hand on hip, made no bones about who she was or what she had to offer: What you see is what you get.
As popular as the expression became, it didn’t morph into its acronym WYSIWYG until technology — again — seemed to require it. Wikipedia dates it to a late 1970’s newsletter called, oddly enough, WYSIWYG, but alas, the good editors at Wikipedia don’t provide an actual reference. The FirstMention of WYSIWYG that I came across was a January 1985 IEEE flyer for the 1st International Conference on Computer Workstations, which burbled very excitedly about new-fangled things like spreadsheets, UNIX, graphic displays, something called miniwini’s, and of course, WYSIWYG editors.