getDarkerColor static method
Implementation
static Color getDarkerColor(Color c, [int percent = 10]) {
assert(1 <= percent && percent <= 100);
var f = 1 - percent / 100;
Color color = Color.fromARGB(c.alpha, (c.red * f).round(),
(c.green * f).round(), (c.blue * f).round());
return color;
}