COLOR

It is evidentiary that color and different colors have different affects on different and maybe even the same things.  For example, the Chakras (if you believe in them) are assigned colors and gemstones that have the relevant color supposedly affects them. 

Let's take the Ruby, which is red carborundum.  It has certain properties.  What are they due to?  The red, the carborundum?  The iron in the carborundum that makes it red? The whole way the crystalline structure is held in array? Or the way the crystalline structure holds the iron atoms in array?

Did you know that blue carborundum is Sapphire?  So, really, Rubies are red sapphires. There are also green sapphires and yellow sapphires and clear (white) sapphires.  So are there properties held in common because these are all a form of sapphire and are there properties that pertain only to the color or are there properties that pertain only to that particular carborundum that contains that particular element to make it a particular color?

Whatever the answer is to this I don't know.  I would suspect, surely, that color is not the only aspect of a gem, but that there is a dual aspect...which of course, takes on three dimensions and probably more, when you look at the whole thing.

So yellow opal and yellow sapphire and yellow citrine may all have some similarity in properties because they are all yellow, but it seems very likely that the underlying structure is where the major benefit lies, and that the color is more of how this energy or emanation or property of a stone is modulated.