PdfColor constructor
Create a color with red, green, blue and alpha components values between 0 and 1
Implementation
const PdfColor(this.red, this.green, this.blue, [this.alpha = 1.0])
: assert(red >= 0 && red <= 1),
assert(green >= 0 && green <= 1),
assert(blue >= 0 && blue <= 1),
assert(alpha >= 0 && alpha <= 1);