I also have the manual version of the 50mm 1.7 and find it produces very true and saturated colors. White balance is quite neutral. Sharpness is excellent and photos from it need little more than the default sharpening, even shooting raw. Unless shooting for fine detail into a very bright background, there's no chromatic aberrations. It has insignificant barrel distortion, and no vignetting from f2 and higher. Some lenses or lens/camera combinations might benefit from a Lightroom preset. No Pentax 50mm prime needs one, especially with your camera.
Using the green button to determine shutter speed, I find it tends to underexpose by a half stop, but that's better caught in the camera than in Lightroom. This is with a K20D.
michael mckee
My Port Townsend – A City in Photographs – 365