getColorAt method
Returns the color at delta
by interpolating between the colors in the list.
Implementation
ColorModel getColorAt(double delta) {
assert(isNotEmpty, 'A color can\'t be returned from an empty list.');
assert(delta >= 0.0 && delta <= 1.0);
if (length == 1) return first;
final slice = 1.0 / (length - 1);
final position = delta / slice;
final index = position.truncate();
final color = elementAt(index);
if (position == index) return color;
return color.interpolate(elementAt(index + 1), position - index);
}