Hi I am not a valuer, but if you are talking about coloured gemstone then you may be able to get an RI if the stone is set high enough. Certainly use the trusty 10 X lens and use a Spectroscope. if it was set low then the valuer may need to take the gem out of the setting.. Most Valuers I know of in Australia would use a Microscope say X 60 to look at inclusions to validate Natural from Synthetic.
I am sure other forum followers would have more info