python color detection from a zone with opencv

I tried to make a color sorter with usb camera and raspberry pi 3 and I got as far as selecting an area in python with opencv but for some reason I can't retrieve the pixels of that area in an array.

import cv2
import time
import pandas as pd
import numpy as np

index = ["color", "color_name", "hex", "R", "G", "B"]
csv = pd.read_csv('colors.csv', names=index, header=None)

cap = cv2.VideoCapture(0)
cap.set(cv2.CAP_PROP_FRAME_WIDTH, 800)
cap.set(cv2.CAP_PROP_FRAME_HEIGHT, 600)

def get_color_name(R, G, B):
    minimum = 10000
    for i in range(len(csv)):
        d = abs(R - int(csv.loc[i, "R"])) + abs(G - int(csv.loc[i, "G"])) + abs(B - int(csv.loc[i, "B"]))
        if d <= minimum:
            minimum = d
            cname = csv.loc[i, "color_name"]
    return cname


while True:
    _, frame = cap.read()
    hsv_frame = cv2.cvtColor(frame, cv2.COLOR_BGR2HSV)
    height, width, _ = frame.shape
    zone = int(16)
    y1 = int((width / 2)+(zone/2))
    x2 = int((height / 2)+(zone/2))
    x1 = int((width / 2)-(zone/2))
    y2 = int((height / 2)-(zone/2))
    selection = frame[y1:y2, x1:x2]
    
    print(selection)
    #cv2.circle(frame, (int(width / 2),int(height / 2)), 5, (255, 0, 0), 3)
    cv2.rectangle(frame, (y1, y2), (x1, x2), (255, 0, 0), 2)
    cv2.imshow("Frame", frame)
    
    key = cv2.waitKey(1)
    if key == 27:
        break
    time.sleep(0.1)
    
cap.release()
cv2.destroyAllWindows()

Can anyone help?