Font colour matching the cell fill

How the text is hidden

Two attributes set independently: the font colour in <font><color/></font> and the cell's fill in <fill><patternFill><fgColor/></patternFill></fill>, both in xl/styles.xml, both reached through the cell's s index into cellXfs. Setting them to the same value — Fill Color then Font Color, two clicks in Excel's ribbon — leaves the glyphs painted and unreadable. White on the sheet's default white ground is the same trick with no fill declared at all.

Why a model still reads it

Colour is a style-sheet property stored in a different part from the text. Cell readers resolve the value or the shared-string index and never consult the font or fill, so the text arrives with nothing marking it as unreadable.

What we do about it

readStyles resolves a font colour from an ARGB rgb attribute or from a <color theme="N" tint="T"/> index against the workbook's theme part — the first xl/theme/themeN.xml in the package, where one is present — falling back independently to the named style in cellStyleXfs when the cell's own format supplies none.

How often it fires

0% of 200 real workbooks from five national open-data portals (CA, IE, DE, GR, UK), measured 2026-08-21.

This is an alert-volume number and nothing else. It says how often the alarm sounds on documents as found — not how often it is right, and not whether what it found was harmless. Documents as found may themselves carry concealment. Read it against the population named above rather than as a property of documents in general.