CSS .device-rect hard-coded stroke + fill, overriding the
stroke=${d.color} SVG attribute the JS wrote. Author CSS beats
presentation attributes, so changing the device colour via the
inspector picker was invisible.
Drop the stroke/fill overrides from .device-rect; set both inline
on the rect element instead — stroke = the chosen colour, fill =
a 12% tint via color-mix so the device reads coloured without
becoming garish. Inline style beats class CSS, so the picker works.
Frames + IO markers don't currently expose a colour picker, so no
analogous fix needed there.