Sorry to bump this, but some posts back
there was some back and forth over the actual color of the Klingon Battlecruiser model on TOS. I today again stumbled across a behind-the-scenes photo of the model on the shooting stage (taken from this site
To my eye there are three colors on this model. A pale purple/lavender color, a darker purplish color on the upper surfaces, and a lighter color on the underbelly.
EDIT BECAUSE TREKBBS CLOSED FOR MAINTENANCE BEFORE I COULD FINISH THE POST
I took the image above and pumped the saturation and noticed right off there is a light greenish color on the inboard side of the nacelle and its supporting strut, and appears to be a tinge of it on the underside of the forward hull. This could either be lighting or an airbrushed greenish cast applied to the "belly" of the model. Could this be lighting? Maybe, but it's coming from an odd direction to apply as much green as it does to surfaces otherwise in shadow. In fact, you'd have to use the palest gel imaginable on a very low watt light to get such a subtle effect, and probably even bounce it off a card to get it to be so soft.
Then there's this picture of Jefferies with one of the models in which it's pretty darned apparent that the upper fuselage of the bulk of the ship is painted a darker shade than the forward 3/4 of the neck and the forward hull. The nacelles are also clearly a lighter shade. This isn't lighting, it's paint. The question remains, is it chromatic paint or achromatic?
None of this is conclusive, but are interesting data points nevertheless.