from tkinter import *
import random
window = Tk()
holst = Canvas(window, width=400, height=400)
holst.pack()
def ranrec(width, height, fcol):    **fcol it's fill color**
    x1 = random.randrange(width)
    y1 = random.randrange(height)
    x2 = random.randrange(x1 + random.randrange)
    y2 = random.randrange(y1 + random.randrange)
    holst.create_rectangle(x1, y1, x2, y2, fill=fcol)
from tkinter import colorchoser **adding submodule**
c = colorchooser.askcolor()
ranrec(400, 400, c[1])