As amateur with old ist ds (ccd) , I like to just shoot camera jpgs and rarely do any post processing.
So I went though a rigmarole like this with color/grey cards:
https://www.box.com/s/po0c0gcvjrg63u3tzn6z
I concluded by comparing the actual cards near a sunlit window with camera jpgs displayed on Eizo monitor and also with RGB readings from Gimp that:
In any sunlight dawn to dusk,cloudy hazy etc, the ist ds is accurate (say within a few parts /127 on the channels).
-Using manual white balance functions on a grey card does not make the camera more accurate in natural light.
-Various M lenses did not show color changes also my only DA lens ( 18~ 55mm kit)
-Some Filters on/off made some color differences, Hoya filters and some others made no measurable difference.
Indoors, most of my shots are not late night so i just use available window light with a mix of window, tungsten, cfl and sometimes low fill flash
In those cases AWB seems to work OK on skin tones.
https://www.box.com/s/c362d247a5d1dd92aa44
here are late night indoor lit shots with AWB
This one is quite accurate
https://www.box.com/s/209edf19081385021670
This one is pure low temperature tunsten lamps with AWB and obviously wrong.
https://www.box.com/s/7426cecc84c150986055