from tkinter import *

root = Tk()

class MyCanvas(Canvas):
  def __init__(self,master,*args,**kwargs):
    self.r = kwargs.pop('radius', 5)
    super().__init__(master=master,*args,**kwargs)
    self.set_bindings()

  def set_bindings(self):
    self.bind("<Button-1>", self.draw_disc)
    self.bind("<Button-2>", self.make_red)

  def draw_disc(self, event):
    x1 = event.x - self.r 
    y1 = event.y - self.r 
    x2 = event.x + self.r 
    y2 = event.y + self.r 
    self.create_oval(x1,y1,x2,y2)

  def make_red(self, event):
    r = 5
    x1 = event.x - r 
    y1 = event.y - r 
    x2 = event.x + r 
    y2 = event.y + r 
    items = self.find_overlapping(x1,y1,x2,y2)
    for i in items:
      self.itemconfig(i, fill="red")

canvas=MyCanvas(root, width=400, height=400, radius=10)
canvas.pack()

root.mainloop()