AnnotationsApi.update()

Changes rect, contents, author, color, fillColor (a square's, circle's or polygon's; refused on anything else) or opacity of the annotation with that id. A color with no alpha changes the color alone; one with an alpha, or an opacity beside it, sets the opacity too; null is refused, a color entry cannot be removed. A new rect moves and scales what the annotation draws — quads, strokes, line ends, a polygon's or polyline's corners — with it; a stamp's or text box's own picture is fitted to it.

update({ color }) rewrites the entry and rebuilds the appearance, so every reader draws the new color. A text box is refused with INVALID_ARGUMENT, since its color is its words'. A stamp accepts the call, but its picture is its own and keeps its colors: only the color entry and the opacity change. update() stamps the modification date when it changes something; it also acts on a reply or a status entry as on any annotation. Needs the annotations feature, and forms too for a form field's widget.