答案1
您可以添加圆弧并填充中间的区域来绘制菱形。
\documentclass{article}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
\draw[very thick, fill=blue!40] (0,0) circle (2);
\draw[very thick, fill=purple!60] (120:2)
arc[start angle=60, end angle=-60, radius=2]
arc[start angle=240, end angle=120, radius=2];
\node at (180:1) {AB};
\node at (0:1) {B};
\end{tikzpicture}
\end{document}