The pulps have always fascinated me. The color seldom seems quite right. The compositions are often a bit off and some of the characterization is just so quirky you can't help but laugh. This is the aesthetic that I feel really allows science fiction to suspend reality. I seldom feel quite so drawn to more technically feasible an image is. Quite frankly, a spaceship is supposed to feel a little bit impossible at times. Some of the characters that Douglas Adams writes about shouldn't be accurately displayed, nor should they be allowed to read poetry to you, but you get my point. Sometimes the campy illustrations make the stories and plots more fun.
Ed Emshwiller is the king of this sort of aesthetic. Take, for instance his cover of Infinity Science Fiction Nov. The beast at the center of his illustrations looks to have absorbed human, insect and dinosaur physiology. The colors of the beast are in that magenta to Prussian Blue that seemed so popular at the time. Meanwhile the background is painted up in a yellow and cobalt teal. The color isn't terribly harmonious and the figures in the background seem a bit disjointed on the whole.
In contrast to this more wild approach, we have his cover for Tom Purdom's "I Want the Stars." This cover is more muted on the whole. The only fully colored and rendered entit y is the spaceman in the light beam. Otherwise the characters and scenery are all line work over a wash. This added contrast really makes this image striking.
I originally found Emshwiller after looking up his cover to Have Spacesuite, Will Travel. The cover is beautiful. This cover, again, has a limited palette. Only a yellow ground with a red figure. Black is added for value. The dichromatic color scheme really seems to intensify the sense of abandonment that Kip felt walking across the moon. Also, the detail in the line work at top indicating a mountain range and craters in the background works so well to frame Heinlein's name.
Lastly, I'd like to speak of the robot on the Cover of Astounding Science Fiction. The character appears so forlorn and yet so simple and mechanical you wonder how it could be indicative of emotion. This is a great illustration.
Enjoy some more of the work of Ed Emshwiller below.
(I do love his strange obsession with Santa Claus being an alien. There are a lot more Santa Claus illustrations if you search for his artwork online.)