void setFillColorRgb(
int r,
int g,
int b,
[num a = 1]
)

Sets the color used inside shapes. r, g, b are 0-255, a is 0-1.

Source

/**
 * Sets the color used inside shapes.
 * [r], [g], [b] are 0-255, [a] is 0-1.
 */
void setFillColorRgb(int r, int g, int b, [num a = 1]) {
  this.fillStyle = 'rgba($r, $g, $b, $a)';
}