An RGB pattern (every built-in one) showed in colour as a pattern fill or
Pattern Overlay in a Grayscale or CMYK document, unlike Edit > Fill, the
export, and Photoshop, which fills in grey but keeps the pattern's colours
(a Grayscale round trip brings them back).
pattern::pattern_rgba projects a pattern's pixels through the document's
mode when painted; the CPU prepared tiles and the GPU pattern textures use
it. Patterns themselves are unchanged.
Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: Brandon Thomas <echelon@gmail.com>
