使用DrawToBitmap把PictureBox转换为一个Bitmap,然后在通过GetPixel方法得到某一个点的颜色
Bitmap picBackGround = new Bitmap(this.pictureBox.Width, this.pictureBox.Height);
this.pictureBox.DrawToBitmap(picBackGround, new Rectangle(0, 0, this.pictureBox.Width, this.pictureBox.Height));
某一点的坐标x,y的颜色
Color currentColor = picBackGround.GetPixel(x,y);