Work the five delivered sources into the pages

The source-request loop paid for itself immediately — two of the five
corrected something rather than confirming it.

The Economist piece settles V1, the riskiest live claim, but our note
had over-claimed: truncating the scale is its *first* example, not one
of "several." Note rewritten to quote her. The same article turned out
to contain a dual-axis chart she caught herself on, now cited.

Datawrapper's color-scale part 1 refuted the assumption behind a queued
sin outright: it makes no argument against rainbow scales and endorses
multi-hue sequential gradients. The rainbow entry is now marked as
having no verified source at all, rather than ample backing.

The dual-axis post independently draws the same line we drew last turn
— of four uses only the alternative-scale case survives, their example
being F against C — and led to two references worth more than the blog
post: the Isenberg et al. study that tested dual-scale charts, and Few's
article working through the cases. Both ship without full metadata
rather than guessed metadata; queued.

Pie and stacked posts gave verbatim support, plus one correction: a
100%-stacked chart has two readable baselines, not one.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01ULE5RRxdQE1ebwefEd2eCM

docs/sources/datawrapper-color-scales.md

@@ -0,0 +1,41 @@
+# Datawrapper — "Which color scale to use when visualizing data" (part 1 of 4)
+
+Lisa Charlotte Muth, `blog.datawrapper.de/which-color-scale-to-use-in-data-vis/`,
+**16 March 2021**. Supplied as PDF, read 2026-08-05. Partly answers queue row 3.
+
+## This does not say what I assumed it said
+
+I had queued this expecting it to condemn rainbow/spectral scales, and wrote in
+the backlog that the series was "the best free treatment of this anywhere" for
+that purpose. **Part 1 makes no such argument.** It is a taxonomy — categorical
+vs sequential vs diverging, classed vs unclassed — and its closing section is
+called "It's not as clear-cut as it seems."
+
+Worse for my assumption, it actively softens the single-hue rule:
+
+> You can use only one hue in your sequential gradients (e.g., light blue to
+> dark blue) – but almost all examples I show here use multiple hues (e.g.,
+> light yellow to dark blue). Using two or even more hues increases the color
+> contrast between segments of your gradient, making it easier for readers to
+> distinguish between them.
+
+So "sequential must be one hue" is **not** a rule we can attribute here, and a
+future rainbow sin must not be written as though multi-hue gradients are the
+problem. The problem with rainbow scales is non-monotonic lightness and implied
+banding, which is a different claim needing a different source.
+
+## What it is good for
+
+- Clean definitions of categorical / sequential / diverging, and classed vs
+  unclassed, if a future sin needs to explain the vocabulary.
+- The framing that a color scale is a *mapping* to data, same as any axis.
+- Its own reference list points at Robert Simmon's *Subtleties of Color* (2013)
+  and Wilke's color-scales chapter — both plausible homes for the actual
+  rainbow argument.
+
+## Still needed for the rainbow sin
+
+Parts 2, 3 and 4 of this series, and Kosara's "How The Rainbow Color Map
+Misleads" (referenced by search results, never read). Re-queued. Until one of
+those is in hand, the rainbow sin has **no** verified source and should not be
+drafted.