Background color for the modal (any valid CSS color can be provided).
For example:
color as text: white, black, blue, red, etc.
RGB as hex: #FF99FF, #330033, etc. (including the hash symbol '#')
RGB as CSS: rgb(153,255,255)
RGBA: rgba(255,255,102, 0.75)
NO EFFECT ON PLAIN INTEGRATION
default: white