Painted covers aren't unheard of, but few publishers in those days stuck to it as a policy like Dell did (but of course, that only applied to certain adventure titles, not to animated and comedic comic books) -- but of course these decisions were made editorially by Western Publishing -- and when Western split from Dell in the early 1960s and re-branded themselves as Gold Key, they maintained the painted cover policy on adventure titles right into the 1970s. Ziff-Davis was another company that had amazing painted covers on its comics. Dell's distribution was better than anyone else's in the 1950s, and they sold more comics as a publisher than just about anyone else. They knew that the cover was the most important tool in selling copies, so they were willing to spend a little extra for a painted cover rather than one with simple colored line art. What's *really* impossible is that Dell gave you a single continuous 34-page story that ran from Page 1 all the way to the back cover -- with no interruptions or advertising. VERY few other publishers gave you so much for one thin dime. Maybe Fawcett, on certain titles.
Link to the book:
Tom Corbett, Space Cadet 06