Gytha Ogg (usually called Nanny Ogg) is a witch and member of the Lancre coven. The character of Nanny Ogg is based on the Mother stereotype of the Triple Goddess myth, and probably influenced by the character Nannie Slag in the Gormenghast series. She's had 5 husbands and been married to three of them and has fifteen children who survived their early childhood (one was born some ten years after the death of her last husband). She has as well innumerable grandchildren and great-grandchildren, but that's incidental; what makes her the Mother is her mentality. People go to Granny Weatherwax for help when they have no choice, but they go to Nanny for advice all the time. Granny is respected, but Nanny is actually liked.
Nanny Ogg has a talent for getting along with people and fitting in. As described in Maskerade, people, after knowing her for fifteen minutes, feel like they have known her all of their lives. Granny Weatherwax knows about this ability, and recognizes its use, and wonders sometimes if it would have been worth acquiring it. Nanny is a lot wiser than Esme (Weatherwax) in some ways, and certainly wise enough not to show it. Gytha Ogg is seen as "one of the people" in a way that Esme isn't. While Granny thinks there's no point in competing if you aren't going to win, Nanny reckons the sympathy you get for being a good runner-up is much better. Granny comes across as judgemental, whereas Nanny has a mind so broad she could tie it under her chin. She appears to be kinder than Granny, but is equally prepared to make tough decisions if necessary.
Death's Domain is a dimension in the Discworld novels, shaped by human expectation and Death's own attempts to have a life beyond his allotted task. It gave rise to a Discworld Mapp of thesame name, drawn by Paul Kidby, with additional material by Pratchett and Stephen Briggs.
The first thing visitors notice is that the Domain is black. Everything in it is black (or different colours and shades of black), except the things that are bone-white. The exceptions are purple mountains in the distance and, since Reaper Man, golden cornfields between the mountains and the Domain proper. Very few living people have entered the Domain, but among the notable exceptions are Albert, Ysabell, Mort, Rincewind, Susan, Twoflower (and, arguably, the Luggage).
Things that are black include all the plants in the garden, the house, the peacocks (although they have white skull-shaped "eyes" on their tails), the cats (Death likes cats) and the bees (Death also likes bees, possibly because a hive mind has no fear of him). Things that are bone-white (and indeed skeletal) include the trout in the pond, some of the birds and the garden gnomes. Death cannot create, he can only copy things. The items in the garden are things he has seen elsewhere, including the fish pond, and presumably the fish inside it.
Although nearly everything in the Domain is black, it is not all the same colour. On the Discworld, and congruent dimensions, splitting darkness with an eight-sided prism produces different colours of black.