Read/Set the text background color for the specified window.
The background color defaults to [0,0,0,0], i.e., a fully transparent black.
This means that the background is invisible. You’ll need to assign at least a
non-zero alpha-value for the background to be drawn. With some text renderers
you’ll also need to enable user-controlled text alpha-blending via a call to
Screen(‘Preference’, ‘TextAlphaBlending’, 1); for text background to be drawn,
e.g., for the Apple OSX legacy text renderer 0. If you want text to be drawn
with sub-pixel anti-aliasing then some renderers need you to set an opaque text
background color - with an alpha value of 255, or whatever the maximum value is
for the selected color mode.