Shapes: Why can't I change the color of the text?

For example, I insert a “sticky note” shape. When I add text, it seems to default to a very light gray. Can I change the color of the copy?

You can change the color (and other font properties) in the STYLE pane : TYPOGRAPHY section, or in the Style Toolbar at top (right-click the menu area and ensure that “Show Style Toolbar” is checked.)

Check this reference documentation for more details: