Drawing a factor graph with colored boxes above the nodes

Question

I was looking at the lecture notes for an online class, and the instructors have some nice pictures for factor graphs and algorithms on factor graphs. One thing that was very helpful were the colored boxes above each node. I was just trying to understand how I would draw something like this. Seems like the nodes would just be circles, as per the the usual tikz base package. But I was not sure how to get those rectangular boxes. Are those from a particular package perhaps?

Answer 1

An empty rectangle split can be used as a label for every circle. And connections with a middle square can be done with the markings library.

\documentclass[tikz, border=1mm]{standalone}
\usetikzlibrary{shapes.multipart, positioning, decorations.markings, arrows.meta}

\begin{document}
\begin{tikzpicture}[
    threeparts/.style={rectangle split, rectangle split parts=3, 
    rectangle split horizontal, 
    draw, rectangle split part fill={#1},
    minimum height=.4cm, outer sep=1mm, inner sep=2pt},
    threeparts/.default={white, white, white},
    mypath/.style={decoration={markings, mark=at position .5 with {\arrow{Square[fill=white]}}},    
                postaction=decorate},
    state/.style={circle, draw, minimum size=1.2cm, fill=#1, anchor=center},
    state/.default=white,
    font=\sffamily
    ]

\node[state=red!30, label={[threeparts={red!30, white, white}]:{}}] (wa) {WA};
\node[state=green!30, label={[threeparts={white, green!30, white}]:{}}, above right=of wa] (nt) {NT};
\node[state, label={[threeparts={white, white, blue!30}]below:{}}, below right=of wa] (sa) {SA};
\node[state, label={[threeparts={red!30, white, blue!30}]:{}}, above right=of sa] (q) {Q};
\node[state, label={[threeparts={red!30, green!30, blue!30}]:{}}, below right=of q] (nsw) {NSW};
\node[state, label={[threeparts={red!30, white, blue!30}]right:{}}, below right=of sa] (v) {V};
\node[state, label={[threeparts={red!30, white, blue!30}]right:{}}, below =of v] (t) {T};

\foreach \i/\j in {wa/nt, wa/sa, nt/q, nt/sa, sa/q, sa/nsw, sa/v, q/nsw, v/nsw} 
    \draw[mypath] (\i) -- (\j);
\end{tikzpicture}
\end{document}

Answer 2

An easy suggestion:

\documentclass[border=3.5mm]{standalone}
\usepackage{tikz}
\usetikzlibrary{positioning}

\begin{document}
    
 \begin{tikzpicture}[thick,node distance=0mm]
    
    %A
    \node at ( 0,0) [circle,draw=blue](A0) {A};
    \node[rectangle,draw=black,fill=green!20,right=of A0,xshift=0.5cm](A1) {};
    \node[rectangle,draw=black,fill=red!20,right=of A1](A2) {};
    \node[rectangle,draw=black,fill=blue!20,right=of A2](A3) {};
    
    %B
    \node at ( 0,3) [circle,draw=blue](B0) {B};
    \node[rectangle,draw=black,fill=green!20,left=of B0,xshift=-0.5cm](B1) {};
    \node[rectangle,draw=black,fill=red!20,left=of B1](B2) {};
    \node[rectangle,draw=black,fill=blue!20,left=of B2](B3) {};
    
    %C
    \node at ( 1,1) [circle,draw=blue](C0) {C};
    \node[rectangle,draw=black,fill=green!20,above=of C0,yshift=0.2cm](C1) {};
    \node[rectangle,draw=black,fill=white!20,left=of C1](C2) {};
    \node[rectangle,draw=black,fill=white!20,right=of C1](C3) {};
    
    \draw [-] (A0) -- (B0);
    \draw [-] (A0) -- (C0);

 \end{tikzpicture}
    
\end{document}