Unless you are talking about stones like onyx and such putting prices
on coloured gemstones can be more difficult than pricing diamonds.
Not only do you have things like cut, clarity and size to consider
but when looking at colour even the natural light that the stone is
inspected under can cause the stone to appear differently eg the
light that occurs in Brisbane is different to that in Adelaide and so
the stone looks brighter in one location than the other.
As an idea see if you can get a price list from Bolton’s in Brisbane
- very descriptive but still only a guide.