Along with the sticker book, Whitman published two coloring books in 1978: UFO Seeing is Believing and UFO Space Strangers. There was also a comic book series the same year, UFO & Outer Space, reprinting select issues of the long-running 1968 series UFO Flying Saucers.
The books followed in the wake of Close Encounters of the Third Kind and shows like In Search of… that sensationalized ‘the unexplained’.
The astronauts of Gemini VII and Gemini X really did sight UFOs. Too bad they weren’t the awesomely kitschy craft seen here.
2 Warps to Neptune 
I am fairly certain that I have a UFO something or other comic book that looks a lot like this artwork. I have to get up in my attic and take a look.