Without seeing the rest of the code, I think the most likely problem is doing all of this before you have the screen initialized. After all, if the screen has not been created yet, where would you expect the input to appear? Here is how I would change it:

import turtle as trtl
troll = trtl.Turtle() 

# Create the screen first
wn = trtl.Screen()
clr = input("give a color pls: ")

# properly use bgcolor as a function from turtle, not a standalone function
wn.bgcolor(clr)
wn.mainloop()