Hey CMD, if you wanna do this method, just make your mask and apply this CodeLab script to the mask layer:
void Render(Surface dst, Surface src, Rectangle rect)
{
for(int y = rect.Top; y < rect.Bottom; y++)
{
for (int x = rect.Left; x < rect.Right; x++)
{
ColorBgra col = src[x, y];
col.A = (byte)(col.R * 0.3 + col.G * 0.59 + col.B * 0.11);
dst[x, y] = col;
}
}
}