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+- Feature Name: `colored-input-output`
+- Start Date: 2024-02-07
+- RFC PR: [lf-lang/rfcs#0003](https://github.com/lf-lang/rfcs/pull/3)
+- Tracking Issue(s): [lf-lang/lingua-franca#0000](https://github.com/lf-lang/lingua-franca/issues/0000)
+
+# Abstract
+[abstract]: #abstract
+
+Magnition mentioned that input and output ports are hard to differentiate if they are placed on the same reactor side.
+
+Additionally, edges become hard to follow in large diagrams.
+This is currently not solved by the edge highlighting mechanism since it highlights the edges by making them thick, which is very hard to spot since a bus is already drawn with a thick line.
+
+# Motivation
+[motivation]: #motivation
+
+We want to add color to make it easier to work with large LF models.
+If elements are very small, color might help us to differentiate them.
+This is even more important if we trade layout stability for edge crossings.
+
+Moreover, I want to test this process with a smaller RFC and see if it fits.
+In my opinion the topic above is something to be discussed and I intentionally put two different things in here, since I do not want to do an RFC for them both and they both affect the color scheme.
+
+# Guide-level explanation
+[guide-level-explanation]: #guide-level-explanation
+
+The different colors for ports and a proper highlighting for edges improve the readability for browsing big hierarchical models.
+
+When browsing large hierarchical models, which are simplified to have same-side input/output ports, adding different port colors additionally improves the readability.
+
+If one wants to follow an edge, you click on it and is highlighted in a bright color.
+This also occurs them clicking the port of an edge.
+
+![](../images/0003_image1.png)
+
+# Reference-level explanation
+[reference-level-explanation]: #reference-level-explanation
+
+This could be added as a hook in the synthesis to add the necessary options and color the elements as required.
+
+# Drawbacks
+[drawbacks]: #drawbacks
+
+Too much color might be distracting and additional synthesis options might clutter the sidebar.
+However, edge highlighting would only occur when one clicks on an edge.
+More synthesis options might not be that distracting once klighd-vscode adds favorites to the sidebar.
+
+# Rationale and alternatives
+[rationale-and-alternatives]: #rationale-and-alternatives
+
+- We could also experiment different port shapes to differentiate the ports.
+- One could also use a different line style to highlight edges. I am however unsure whether this is enough if drawn line is very thin (since the diagram itself is big).
+
+# Prior art
+[prior-art]: #prior-art
+
+- SCCharts uses a light blue to highlight clicked edges
+- The large LF models that Magnition is working with pose real, practical UX challenges.
+
+
+# Unresolved questions
+[unresolved-questions]: #unresolved-questions
+
+- I would suggest either a blue or orange for highlighting
+- Colors for ports are still up for discussion, maybe black for input and black border with white fill for outputs?
+
+# Future possibilities
+[future-possibilities]: #future-possibilities
+
+This would be the first step to optimize LF for large models that might be used in industry.
+
+I needed roughly 30min for this RFC, just as a reference.
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