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wb_apply_cell_styles() and wb_apply_border() passed flextable's color
strings straight to openxlsx2::wb_color(). R writes a color with an alpha
channel as #RRGGBBAA, but Excel reads eight hex digits as AARRGGBB, so
the alpha byte became the red channel: a translucent yellow such as
"#EDB50199" (adjustcolor("#edb501", 0.6)) exported as purple, and a
half-transparent black border as dark blue.
Font colors were already normalised through prepare_color(); fills and
borders now go the same way. prepare_fill_color() wraps it so that
"transparent" survives as "transparent" for the existing no-fill check.
Adds a regression test asserting the opaque FFRRGGBB value for a fill
and a border with alpha, and that a named color and an unfilled cell are
unchanged.
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Fixes #47
The problem
wb_apply_cell_styles()andwb_apply_border()pass flextable's colour strings straight toopenxlsx2::wb_color(). R writes a colour with an alpha channel as#RRGGBBAA, but Excel reads eight hex digits asAARRGGBB, so the alpha byte lands in the red channel and the colour shifts by one byte. A translucent yellow such as#EDB50199(adjustcolor("#edb501", 0.6)) exports as purple; a half-transparent black border exports as dark blue. Nothing errors, the colours are just wrong.Font colours do not suffer from this because
wb_apply_content()already normalises them throughprepare_color(). Fills and borders skipped that step.The fix
wb_apply_cell_styles()goes through a newprepare_fill_color(), a thin wrapper aroundprepare_color()that keeps"transparent"as"transparent"(whereprepare_color()returnsNA), so the existing!= "transparent"guard keeps working.border.color.*columns inwb_apply_border()go throughprepare_color()after the existingtransparent -> blacksubstitution.Both use
grDevices::col2rgb()under the hood, so named colours,#RRGGBBand#RRGGBBAAall reduce to the opaque#RRGGBBthatwb_color()turns intoFFRRGGBB. Excel has no translucent solid fills, so dropping the alpha is the only faithful option; it matches what font colours already do.Tests
Added a regression test in
test-wb_apply_cell_styles.Rthat exports a fill and a border with alpha and asserts the opaqueFFEDB501/FF000000in the style XML, that a named colour (orange) is unchanged, and that an unfilled cell stays unfilled. It fails onmain(Expected style_of("A2", "fill") to match "rgb=\"FFEDB501\"", actualrgb="EDB50199") and passes with the change. The full suite is green locally, with only the pre-existing CRAN-gated andflexlsxtestdirskips.NAMESPACEalready importsdplyr::coalesce, so no roxygen run is needed for the new helper.I added a NEWS bullet under a development heading; happy to drop or reword it.
Note: This fix was produced with the help of Claude