Denim, deep blue, polished nugget of Indian Sapphire. He has not only a universally good color (almost everybody wears jeans) but also hardness!

color is natural

Sapphire is a stone of kings, and its blue variant is one of the most desirable (and also most expensive in the case of transparent versions) gems at all, one of the stones of the third eye, the sphere of decision-making and intuition. it is a very strong stone, like all corundum. (also very persistent)

it is possible to drill through it (the price of sapphire drilling is 20, - CZK due to their extreme hardness)