Usually these stones are acceptable only if the material is very rare or the price is very low. None are offered on this site. It is NOT a synonym for deep or dark. A stone can be deep, but not saturated and saturated without being dark. Often facet meets and polishes are imperfect.
Styles are usually ovals or cushions.
It shows excellent symmetry, a well proportioned crown, good facet meets, a fine polish and no window. In these cases, however, something other than maximum brilliance was being sought. All gems, on this site unless otherwise labelled are custom cut. A window is an area under the table of a stone that does not reflect light. It's called a window because light goes through it like window glass.