As a kid in the 60's, I was terrified by three movies (other than The Killer Shrews), but I can't remember their names.
The first was about robots overtaking a city. There were human-size bots and one giant bot, all with single eyes that looked like small tv screens. They went about, frying everything in sight.
Second was a movie about giant crabs and a mutant cyclops on an island.
The third was about a small flying saucer with a small alien robot, who attacked a lady with a knife.
I know, I know, I am truly NUTS. But as a kid, watching these flicks gave me nightmares for weeks. I think my own kids would get a good laugh....
That would be....(drumroll, puh-leeze).....
The Twilight Zone episode entitled The Invaders, it starred Agne Moorehead and featured a classic score by Jerry Goldsmith.
Oof. Your memories might be mixing Mysterious Island (giant crab) with The Seventh Voyage of Sindbad (cyclops), or Attack of the Crab Monsters or even Bert I. Gordon's The Cyclops, which featured assorted giant bugs in addition to the title mutated human. Attack and Cyclops are B&W, Mysterious and Golden are color.
The first one might be Target Earth, but I've never seen it and don't recall a giant robot being described in it...Earth Vs. The Flying Saucers has man-sized armored aliens that resemble robots--without the "eye" you describe--frying everything, but no giant 'bot (instead, saucers with arm-like guns shoot up everything)...
The second one could be Corman's "Attack Of The Crab Monsters".
The first is clearly TARGET EARTH, the second Bert I. Gordon's THE CYCLOPS, and the third the aforementioned episode of THE TWILIGHT ZONE. Yeah, some of the remembered details are faulty, but heck, don't we all have that problem?
I have a reader review over at my site of THE CYCLOPS (complete with pics). It may help you definitively identify whether or not this is indeed your mutant cyclops movie:
http://www.scifilm.org/reviews/cyclops.html
I think that the snake from "The Cyclops" would be the same tired snake that was the title star in "Serpent Island." Except he was prone to jumping (well, once) in the latter movie.
Andrew