I have a large hunk of aquamarine, about 20-30 karats but the hew changes where its naturally faulted from light blue on one side to dark or medium on the other
Aquamarine is normally a light toned greenish blue hue though some material, specifically from Brazil has been found without the green secondary hue. With aqua the darker the tone the better provided there is no grayish mask. If window glass is 0% tone and coal is 100% tone most aquamarine will be somewhere between 10-30%. 40% plus gets into the finer grades.
RWW