Color writes copy values in tag order, then deliver superclass
notifications before changing the screen color. Component writes add an
RGB notification; RGB writes add all three component notifications,
using final stored values before the original tags. Equal values are not
suppressed. When set up with a screen and no no-pen flag, SetRGB32
recolors the stored pen; redraw is requested only above depth eight.
Other users of a fixed pen can therefore change appearance too.
Pen replacement releases any locally allocated pen but does not allocate
a replacement in OM_SET. Setting a sentinel does not clear an
already-set fixed-pen flag. A no-pen flag from a failed allocation is
not cleared by an ordinary subsequent Pen or RGB set. These are
implementation limitations, not a guarantee of switching between
automatic and fixed modes.