The older CCD sensor Pentax cameras - e.g. the K10D - reproduce colours differently than the later CMOS cameras. It's very clear when comparing RAW files from both types of camera in something like Lightroom. Whether that's to do with the sensor or in-camera processing is debatable, but that doesn't really matter. When all's said and done, there's a difference, and quite a lot of people prefer the output of those older CCD cameras, whatever the technical reasons.
It's possible to more-or-less recreate the CCD cameras' colours and tone curve with pretty much any camera by tweaking the hue, saturation and luminance of individual colours in post-processing. I put a lot of time into developing a preset for Lightroom that does just that, for use with my K-3 and K-3II. It gets very close to re-creating the output of a K10D...
All that said, I still choose to shoot an old GX-10 (K10D clone) regularly, as I like the straight-out-of-camera colours and overall look of the images it produces