Field note · April 29, 2026
Course note — Colour is an encoding, not decoration
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.
Revised Colour is an encoding, not decoration this week. The change was small and the reason was not.
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 first draft explained the mechanism and stopped. What was missing was the failure: the thing that happens when you get it wrong, described concretely enough that someone recognises it later. A lesson that only teaches the correct version leaves you unable to spot the incorrect one, which is the situation you will actually be in.
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.