See makeBgWhiteSpt(), makeBgBlackSpt()

toggleIsDown[backgroundIndex] is used for tests instead of the actual background color.
Note [] not ()
see e.g. getEchoColor();

setButtonState("down", backgroundIndex)

Jmol variable backgroundColor

N.B. setButtonState("up", backgroundIndex); ALSO BLACKS BKG OF PDBID ECHO!