How do I set only one side of a tikz node's border color?

Question

I want to have a node with different border colors: One for the upper and left border, one for the lower and right color.

Is this possible? From all examples I found, it seems that I can only set the color as a whole, not for each side.

There is a duplicate of this but I don't know what to search for :) — percusse, Sep 07 '14 at 12:07
@percusse This: Tikz shape similar to rectangle with selective drawing of borders ? — , Sep 07 '14 at 12:17
@HarishKumar Sure, but it should be reproducible with arbitrary node sizes. I thought about drawing two triangles in the background and setting the node above them using the fit package, but I guess I would get problems with deeper nesting when I do this. — flyx, Sep 07 '14 at 12:32
I think it's not a duplicate but can help: http://tex.stackexchange.com/questions/10980/tikz-changing-colour-of-a-path-half-way-along?lq=1 — Ignasi, Sep 09 '14 at 10:43
@percusse: Was your answer to different-colours-for-tikz-node-frame-sides what you were looking for? — Ignasi, Sep 09 '14 at 10:52
@alper I'm sorry, the file seems to have been lost to some server migration. — flyx, Jul 22 '22 at 17:55

score 8 · Accepted Answer · 2014-09-07T12:59:48.477

This should get you started. More polishing can be done, but left as an exercise.

\documentclass{article}
\usepackage{tikz}
\tikzset{%
pics/.cd,
mynode/.style args={#1#2#3}{
  code={\node (a) {#3};
       \draw[thick,#1] (a.south west) |- (a.north east);
       \draw[thick,#2] (a.south west) -| (a.north east);
  }
},
}
\begin{document}
  \begin{tikzpicture}
    \pic {mynode={red}{blue}{Here}};
    \pic at (4,0) {mynode={olive}{magenta}{Here comes another one}};
  \end{tikzpicture}
\end{document}

enter image description here

\documentclass{article}
\usepackage{tikz}
\tikzset{%
pics/.cd,
mynode/.style args={#1#2#3}{
  code={\node (a) {#3};
       \draw[thick,#1,line cap=butt,shorten <= -0.5\pgflinewidth,shorten >= 0.5\pgflinewidth] (a.south west) |- (a.north east);
       \draw[thick,#2,line cap=butt,shorten <= 0.5\pgflinewidth,shorten >= -0.5\pgflinewidth] (a.south west) -| (a.north east);
  }
},
}
\begin{document}
  \begin{tikzpicture}
    \pic {mynode={red}{blue}{Here}};
    \pic at (4,0) {mynode={olive}{magenta}{Here comes another one}};
  \end{tikzpicture}
\end{document}

enter image description here

Thanks! I'm not sure what to do about the ugly corners where the colors meet, but I'll try to fix that myself. — flyx, Sep 07 '14 at 12:46
Your code may be correct mathematically, but it produces a small gap between the lines when I render it. I could use a factor slightly smaller than 0.5, but the gap has a different width depending on the zoom level, so this is not the solution. I need a way to actually connect the lines with each other. — flyx, Sep 09 '14 at 18:44

How do I set only one side of a tikz node's border color?

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