tint.js

var source = [255,128,0]; // orange-ish

// get pixels from canvas
for (i = 0; i < pixels.data.length; i += 4) {
  brightness = ((3*pixels.data[i]+4*pixels.data[i+1]+pixels.data[i+2])>>>3) / 256;

  pixels.data[i] = ((source[0] * brightness)+0.5)>>0;
  pixels.data[i+1] = ((source[1] * brightness)+0.5)>>0
  pixels.data[i+2] = ((source[2] * brightness)+0.5)>>0
}

// pixels now tinted to orange