Every colour input opens one picker laid out like After Effects' Color
Picker: a square and slider for the channel chosen with H / S / B /
R / G / B, the new colour over the original, HSB and RGB fields, a hex
field (#RRGGBB, RRGGBB, #RGB) and OK / Cancel. Changes apply live;
Cancel, Escape and the original swatch restore the starting colour.
The 3D light dialog, Essential Graphics and Layer Styles passed sRGB
values to egui's color_edit_button_rgb(a), which reads them as linear,
so picked colours were stored darker (#808080 became #373737). They and
the other dialogs now use the shared sRGB colour button.
The picker and colour helpers live in color_picker.rs; widgets
re-exports them.
Tests: ui_color_hex.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>