Where means are you from a city or rural area, more importantly, are you Northern or Southern. This is really where the When comes in. If yes, the where doesn't really matter much, but if you are doing late war, the blockade would have a definite effect on the availability of mourning materials as well as most other materials. Lighter mourning means initially adding more white to the black and less crape trim. Gradually adding other mourning colors such as gray, lavender, purple and more white as time passes allows a woman to reenter full society again.
Jewelry has it's own rules.
Full mourning requires only a jet, hard rubber or other black jewelry at most. Lighter mourning allows for small amounts of gold, pearls, diamonds, etc. Whenever you see a woman in all black, don't assume she's a widow. She may be wearing a fashionable black dress, especially if it's shiny black and fashionably trimmed. Even if she is clearly wearing mourning black, she could be in mourning for a relative or other very close person.