Python - PyGame - keep ciicked (Stackoverflow)

#!/usr/bin/env python3

# date: 2025.05.29
# stackoverflow: [python - PYGAME Circle changes colour on clicking but changes back on mouse up - Stack Overflow](https://stackoverflow.com/questions/79639247/pygame-circle-changes-colour-on-clicking-but-changes-back-on-mouse-up)

import pygame
import random

# --- constants ---  # PEP8: constants after imports

# display window
SCREEN_HEIGHT = 800
SCREEN_WIDTH = 1400

# colours
BLUE = (0, 0, 255)
LIGHTBLUE = (72, 243, 235)
BLUEBLACK = (20, 21, 77)
IODINE = (243, 200, 99)
REDYELLOW = (221, 78, 20)
BLACK = (0, 0, 0)

# other
X = 500
Y = 400

SIZE = 40
X_SPACING = SIZE*2.3
Y_SPACING = SIZE*2.3

# --- classes ---  # PEP8: classes after constants

class Experiment():
    def __init__ (self, colour, x, y, size, number):
        self.x = x
        self.y = y
        self.size = size
        self.number = number
        self.colour = colour

        self.rect = pygame.Rect(self.x-self.size, self.y-self.size, self.size*2, self.size*2)

        self.clicked = False

    def draw(self, screen):
        #pygame.draw.rect(screen, LIGHTBLUE, self.rect)

        if self.clicked:
            pygame.draw.circle(screen, BLACK, (self.x, self.y), self.size )
        else:
            pygame.draw.circle(screen, self.colour, (self.x, self.y), self.size)
            pygame.draw.circle(screen, BLACK, (self.x, self.y), self.size, 4)

    def handle_event(self, event):
        if event.type == pygame.MOUSEBUTTONDOWN:
            if self.rect.collidepoint(event.pos):
                self.clicked = True

# --- functions ---  # PEP8: functions after classes

# --- main ---  # # PEP8: main code after functions

# - variables -

wellcolour = IODINE
colour = IODINE

# - init -

pygame.init()

screen = pygame.display.set_mode((SCREEN_WIDTH, SCREEN_HEIGHT))
pygame.display.set_caption('Amylase')

# - create all instances only once, using for-loop, and keep them on list

items = []

for row in range(4):
    wellcolour = (243, row*40+100, 99)
    for col in range(5):
        x = X + (col * X_SPACING)
        y = Y + (row * Y_SPACING)
        number = col + (row * 5) + 1

        item = Experiment(wellcolour, x, y, SIZE, number)

        items.append(item)

# - main loop -

run = True

while run:

    # - events -

    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            run = False
        # send every event to all items
        for item in items:
            item.handle_event(event)

    # - updates (without drawing) -

    # update all items
    # for item in items:
    #     pass  # empty function

    # - draws (without updates) -

    screen.fill(LIGHTBLUE)

    # draw all items
    for item in items:
        item.draw(screen)

    pygame.display.flip()

# - end -

pygame.quit()