First time grower. Darkening buds around pistols, anything to worry about?

Looks fine to me. Some plants get purple from genetics and some can get darker because of cold. Usually the genetic ones the purple starts at the middle and from the cold on the edges of leave and tips of calyxes, so you have probably just had cooler night temps. It's from anthocyanins in the plant. Hopefully the budrot stays away, just keep an eye out for leaves in the buds turning yellow. It almost always starts inside the flower and a leaf or 2 dying can be a sign that the budrot has started attacking the petiole and flower.