Every node is either red or black.
If a node is one color, its child is the opposite color.
Every path from a given node to leaf nodes contains the same number of black nodes.
See this YouTube video for more information about Red-black tree insertions. We are looking at one specific case in this webpage.
https://youtu.be/5IBxA-bZZH8?si=CJ8c1pDFZQ3Nl79P&t=115Here is an image of a Red-black tree color violation with a red uncle.
Color Violation with Red Uncle