Sets the background color of the image viewer. It is a value specifying the 32-bit RGBA value.
iValue: the value to set
Default is transparent (0x00000000). The byte-ordering of the 32-bit RGBA value is RRGGBBAA. RR represents red, GG represents green, BB represents blue, AA represents opacity, ranging from 0 to 0xFF. 0 is transparent, 0xFF is non-transparent.
In the browser, opacity ranges from 0 to 1. We will convert it automatically, therefore, sometimes the value you get after setting it might be slightly different.