Color code input, output, and in-out models

We have slightly different design rules for input, output, and in-out models. It would be useful to color code (or equivalent) types that:
1. are used as only inputs.
2. are used as only outputs.
3. are used as both inputs and outputs.

No files, tests, or entry points are identified in the issue. First locate the tool or visualization that represents input and output models, then determine how it identifies models used only as inputs, only as outputs, or as both; done means those three categories are visibly distinguishable.

Written by the indexing model from the issue text.