TikZ - Parallelogram Vector Rule

\documentclass[tikz]{standalone}
\usepackage{libertinus,microtype,xcolor}
\colorlet{cyanish}{cyan!25!}
\usetikzlibrary{calc}
\begin{document}
   \begin{tikzpicture}
\coordinate (A) at (0,0);
\coordinate (B) at (3,2);
\coordinate (C) at (6,1);

\coordinate (b) at (3,-1);

\draw[-stealth] (A) --node[sloped,above]{\(\vec{a}\)} (B);
\draw[-stealth] (B) --node[sloped,above]{$\vec{b}$} (C);
\draw[-stealth,gray] (A) --node[sloped,above]{\(\vec{b}\)} (b);
\draw[-stealth,gray] (b) --node[sloped,above]{\(\vec{a}\)} (C);
\draw[-stealth,red] (A) --node[sloped,above]{\(\vec{r}\)} (C);

\node[blue,anchor=south] at (B) {\(\alpha\)};
\begin{scope}
\clip (A) -- (B) -- (C) --cycle;
\draw[blue] (B) circle [radius=2.5mm];

\draw[red] ($(A) + (0.2,0.2)$) circle [radius=4mm];

\end{scope}

\begin{scope}
    \clip (A) -- (B) -- (C) -- (b) -- cycle;
    \draw[orange] (A) circle [radius=3mm];
\end{scope}

\node[orange,anchor=east] at (A) {\(\theta\)};

\node[red] at ($(A) + (0.8,0.27)$) {\(\gamma\)};

\node[draw,align=left] at (2.8,-2) {\textcolor{orange}{\(\theta = \text{Angle between vectors}\)}\\
\textcolor{blue}{\(\alpha =\)Angle between vectors in parallelogram}\\
\textcolor{red}{\(\gamma =\)Angle of resultant vector}};
\end{tikzpicture}
\end{document}