I am trying to convert RGB to Lab and then zero the a and b channels to get a grayscale image but I get an image with reddish orange tint

Question

My code:

imgrey = np.asarray(ibuffer).copy()
grey = cv2.cvtColor(imgrey, cv2.COLOR_BGR2Lab)
grey[:,:,1] = 0
grey[:,:,2] = 0
grey = cv2.cvtColor(grey,cv2.COLOR_LAB