I don't find the use of gemstones to be restricted to a certain type of magick, anyone can use them in any path they follow.
As for colors of magick, that is a topic that gets very heated and often degrades into a fight.
From what I have heard over the years,
black - any thing that hurts another
white - anything that helps another
green - having to do with plants
brown - having to do with plants and animals, earth
I personally find those to be oversimplifications of a complex subject. Magick comes from energy, energy is neutral. The intentions of a caster are what matter. However it seems that the color assigned to the magick is often not determined by the caster but by those who are outside the situation, especially with the black and white. Black and white have become moral judgments on the actions of another. Bad people cast black magick, good people cast white magick. I find this self serving. I will cast the spell that I find to be useful or warranted in the situation I feel needs a spell. If I determine a hex or curse is what is called for, that is what I cast. If I determine protection or healing is called for, that is what I cast. I am neither a white witch or a black witch (referring to the color classification of magick) I am a witch. End of story.
Those who choose to identify as either a white witch or a black witch are free to do so, however when they choose to label me or anyone else than they have crossed a line as far as I am concerned.
Back to the stones, I use stones in many things. I use them to make pendulums for divination. I use them as offerings. I use them to enhance certain spells. I have a few that are charged to help me center and focus when things are stressful in my life. Stones are components of spells, they have different attributes that can be used in whatever combination the user requires or desires. Some are just collected because they are pretty. Rose quartz when placed around pink candles can help to increase a love spell. Quartz I find to be useful in almost any spell I cast, also works great for charging with a luck spell or protection spell as a gift for a friend. Onyx is wonderful, in my opinion, of attracting and holding negative energies that are directed at a person or that seem to surround them, best to bury the stone after a time to keep the energies from seeping back to the person.
Hope this gave you some insight into how I view things.