Reader question — Colour is an encoding, not decoration

Reader question on Colour is an encoding, not decoration, and the answer belongs somewhere more findable than an email.

Colour has exactly four jobs in a chart. Using it for anything else adds noise, and using it carelessly excludes about one in twelve of your readers.

The question was, roughly, "when does this stop applying?" — which is the right question and the one lessons routinely fail to answer. Every technique has a range of validity, and stating it is what separates a lesson from a recipe.

It sits in the Showing the result module. The exercise is a thinking one rather than a query one — some of this material is about deciding what to compute, and that does not need a keyboard.

Ordering matters here more than in most courses. It follows Choosing the form before the colours and leads into Communicating a result to someone who will not read your notebook, and reading it out of sequence mostly works but costs you the setup.

Free means free, and it also means we can rewrite it whenever it is wrong. No edition, no errata PDF, nothing to repurchase. The whole course is 36 lessons and the fixes land the day we find them.