Backgrounds are automatically converted to text display entities when possible (1.19.4+), in those cases transparency is supported. Transparency can be defined as an r g b a color value, for example color: 255 0 0 128.
Background
## object name, you can set this to anything that is uniquebackground1:## object type, in this case backgroundtype:background## x and y positions relative to the parentposition:0 0## width and height of the objectsize:max max## color of the backgroundcolor:white