Create a color from red, green, blue, and opacity, similar to
rgba() in CSS.
ris red, from 0 to 255.
gis green, from 0 to 255.
bis blue, from 0 to 255.
opacityis alpha channel of this color as a double, with 0.0 being transparent and 1.0 being fully opaque.
Out of range values are brought into range using modulo 255.
See also fromARGB, which takes the opacity as an integer value.
const Color.fromRGBO(int r, int g, int b, double opacity) : value = ((((opacity * 0xff ~/ 1) & 0xff) << 24) | ((r & 0xff) << 16) | ((g & 0xff) << 8) | ((b & 0xff) << 0)) & 0xFFFFFFFF;