Usually the diamond stud earrings rough will be cut into whichever shape that requires the least amount of sacrifice. Marquise and oval shapes should have a length thats exactly twice the size of the width. If they are too narrow or too wide, the stone will loose light and appear too dark.
Most of the diamond stud sold today come from Africa, but Australia and Russia are suppliers of uncut diamonds as well.
platinum wedding ring experts would never attempt to verify a diamonds color in a setting, and would insist on a certified color comparison before attempting to make a fair evaluation, confirming how difficult differences in color grades are to see.