Changing color of initial state in tikzpicture automata on a per-node basis

Question

When using the initial state with the automata drawing library for the tikzpicture environment, I have been unable to find a way to change the color of the initial state on a per-node basis.

That is, I want to be able to have different colors for initial states in the same instance of a tikzpicture environment.

I would also be fine with the creation of a style or workaround that doesn't directly use the initial state but functionally and visually looks the same.

For example, in the LaTeX below, I am able to do this on a tikzpicture environment basis, but I would like to be able to modify it on a per-node basis:

\documentclass{article}
\usepackage{tikz}

\usetikzlibrary{arrows, automata}

% The pgfkey for creating graphs used in tikzpicture
\tikzset{
    discrete graph/.style={
        ->,
        >=stealth',
        auto,
        thick,
        main node/.style={circle, draw, font={\sffamily\bfseries\Large#1}},
        nolooparrow/.style={-, every loop/.append style={-}},
        double arrows/.style args={##1, ##2, ##3}{
            decorate,
            decoration={
                markings,
                mark=at position 0 with {
                    \coordinate (ta-base-1) at (0, ##3pt);
                    \coordinate (ta-base-2) at (0, -##3pt);
                },
                mark=at position 1 with {
                    \draw[##1] (ta-base-1) -- (0,##3pt); \draw[##2] (ta-base-2) -- (0,-##3pt);
                }
            }
        },
        every node/.style={font=\sffamily\small},
    },
}

\begin{document}
    
    \begin{tikzpicture}[discrete graph=\normalsize, node distance=2.5cm]
        \node[main node, state, initial] (a) {$q_0$};
    \end{tikzpicture}
    
    \begin{tikzpicture}[discrete graph=\normalsize, node distance=2.5cm, every initial by arrow/.style={red}]
        \node[main node, state, initial, red] (a) {$q_0$};
    \end{tikzpicture}
    
\end{document}

Answer 1

Perhaps the easiest is to draw the arrows for the additional initial nodes manually, and set them to the desired color.

The distance between the text and the node in the code below is set to 3ex, which is the default in the automata library.

MWE:

\documentclass{article}
\usepackage{tikz}

\usetikzlibrary{arrows, automata, positioning, decorations.markings, calc}

% The pgfkey for creating graphs used in tikzpicture
\tikzset{
    discrete graph/.style={
        ->,
        >=stealth',
        auto,
        thick,
        main node/.style={circle, draw, font={\sffamily\bfseries\Large#1}},
        nolooparrow/.style={-, every loop/.append style={-}},
        double arrows/.style args={##1, ##2, ##3}{
            decorate,
            decoration={
                markings,
                mark=at position 0 with {
                    \coordinate (ta-base-1) at (0, ##3pt);
                    \coordinate (ta-base-2) at (0, -##3pt);
                },
                mark=at position 1 with {
                    \draw[##1] (ta-base-1) -- (0,##3pt); \draw[##2] (ta-base-2) -- (0,-##3pt);
                }
            }
        },
        every node/.style={font=\sffamily\small},
    },
}

\begin{document}
    
\begin{tikzpicture}[discrete graph=\normalsize, node distance=2.5cm, every initial by arrow/.style={red}]
\node[state,initial,red] (q_0) {$q_0$};
\node[state,blue]             (q_1) [above right=of q_0] {$q_1$};
\node (start2) [left=3ex of q_1,blue] {start}; % extra start label
\draw[->,>=stealth',blue] (start2) -- (q_1); % extra start arrow
\node[state]             (q_2) [below right=of q_0] {$q_2$};
\node[state,accepting]   (q_3) [below right=of q_1] {$q_3$};

\path[->] (q_0) edge node {0} (q_1)
                edge node [swap] {1} (q_2)
          (q_1) edge node {1} (q_3)
                edge [loop above] node {0} ()
          (q_2) edge node [swap] {0} (q_3)
                edge [loop below] node {1} ();
\end{tikzpicture}    
\end{document}

Result: