The relationship between sample colour and voltage is as follows:

colour = -w.log10 ((Vsample-Vzero)/(Vsolvent-Vzero))

where: Vzero is the circuit voltage at zero transmission; Vsolvent is the measured voltage of the carrier solvent (in this case water) ; Vsample is the measured voltage of the coloured liquid sample; and, w is a multiplier and correction factor for the path length of the light as it passes through the sample holder. To simplify the math, Vzero could be manually adjusted to read zero voltage on zero transmission, I guess.

Basically I'd prefer to develop this as an all analog device. I've seen arduino and pic based solutions, but I don't want to follow that route.

What I'm currently wrestling with is the post voltage measurement side.

My question can be simplified to this: How do I translate the above formula into a simple, analog computational circuit and subsequently display that result in a meaningful manner?

Currently I've been looking at some logarithmic circuits and examples, here and as well as elsewhere, but I haven't seen anything quite like my specific application and I'm starting to sink a little. Any chance of some help?