On GTK desktops (Mint, XFCE, GNOME) Qt hands QColorDialog to GTK's
chooser. Its "Custom" row is a recent-colours list kept by GTK: every
colour picked is pushed in on the left and the oldest drops out, so a
user's saved wire colours are lost (forum topic 3190). It also ignores
the custom colours QET saves (#918) and has no swatch grid for the
double-click to accept (#1172).
Pass DontUseNativeDialog at every colour dialog, so all platforms get
the dialog Windows already shows: 16 custom slots that change only on
"Add to Custom Colors", saved across restarts.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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