onRgb16m method Null safety

Chalk onRgb16m(
  1. num red,
  2. num green,
  3. num blue
)

Create Chalk with a background color with the specified RGB values (forces using ANSI 16m SGR codes, even if level is not 3).

Implementation

Chalk onRgb16m(num red, num green, num blue) =>
    makeRGBChalk(red, green, blue, bg: true, force16M: true);