This Pentax lens is not that exotic, glasses had progressed by the time of its manufacture. Looking at the colour of the multicoating is actually too ambiguous, as long as the glass & coatings are in good condition you have a lens made to far tighter tolerances than many manufactured today.
Pentax Spotmatic cameras & lenses were wonderfully over engineered and possibly only Leice cameras are on a similar par with regards to build quality.
[QUOTE)]he is an allumini of both the Leica and Pentax service departments, he said it was the coating. For piece of mind on my part what tone of yellow should I look out for on my lens?