The 512Ke was offered in platinum from March 1987 - September 1987 if memory serves me right. The entire product line had gone to platinum except the Apple IIc (the Plus, IIe, and ImageWriter II all lost their beige or white cases in early 1987).
A platinum 512Ke basically looks like a platinum Plus but has no words on its front bezel. The back has the familiar "Macintosh 512K" badge used on other 512Ks and 512Kes since 1984.
Apple kept this model around as the low-end back when the Plus was still rather new and the SE and II had displaced it as the best Mac in the stable. Remember, the 512Ke was around as a cheaper alternative to the Plus in 1986 (I believe it was code-named the "Mac Minus"). I wouldn't call all 512Kes rare, just the platinum ones. It's relatively easy to find a beige one--pretty much any 512K made from mid-1986 onward will be a 512Ke. (You'll also find a lot of upgraded 512Ks that didn't start their lives as 512Kes, but a quick check of the serial number can verify things--if it's F612... or thereabouts it's probably always been a 512Ke).
A platinum 512Ke basically looks like a platinum Plus but has no words on its front bezel. The back has the familiar "Macintosh 512K" badge used on other 512Ks and 512Kes since 1984.
Apple kept this model around as the low-end back when the Plus was still rather new and the SE and II had displaced it as the best Mac in the stable. Remember, the 512Ke was around as a cheaper alternative to the Plus in 1986 (I believe it was code-named the "Mac Minus"). I wouldn't call all 512Kes rare, just the platinum ones. It's relatively easy to find a beige one--pretty much any 512K made from mid-1986 onward will be a 512Ke. (You'll also find a lot of upgraded 512Ks that didn't start their lives as 512Kes, but a quick check of the serial number can verify things--if it's F612... or thereabouts it's probably always been a 512Ke).