How can I fill in my Shape in Python with Turtle?

I would like to fill in my Shape that I have created with the turtle module in python. I have figured out the outlines and the Turtle itself, but I don`t know how to color in the finished shape. This is my code so far:

    trtl.fillcolor("green")
    trtl.shape("turtle")
    
    if currentdepth == depth:
        trtl.forward(length)
    else:
        currentlength = length/3.0
        trtl.pencolor("Blue")
        koch_segment(trtl, currentlength,currentdepth + 1)
        trtl.left(60)
        trtl.pencolor("Red")
        koch_segment(trtl, currentlength, currentdepth + 1)
        trtl.right(120)
        trtl.pencolor("Green")
        koch_segment(trtl, currentlength, currentdepth + 1)
        trtl.left(60)
        trtl.pencolor("Orange")
        koch_segment(trtl, currentlength, currentdepth + 1)



    wn = turtle.Screen()
    wx = wn.window_width() * .5
    wh = wn.window_height() * .5
    base_lgth = 2.0 / math.sqrt(3.0) * wh       # is the base length dependant on the screen size
    myturtle = turtle.Turtle()
    myturtle.speed(0.5 * (depth + 9))           # value between 1 and 10 (fast)
    myturtle.penup()
    myturtle.setposition((-wx / 2, -wh / 2))    # start in the lower left quadrant middle point
    myturtle.pendown()
    myturtle.left(60)

    return myturtle, base_lgth```

Solution

Since you are trying to fill a recursive drawing function, we probably need to do the fill commands around the initial call to that function. Working with the code you posted, it would be something like:

from turtle import Screen, Turtle

DEPTH = 4
LENGTH = 300

def koch_segment(turtle, length, currentdepth):

    if currentdepth == 1:
        turtle.forward(length)
    else:
        currentlength = length/3

        turtle.pencolor('blue')
        koch_segment(turtle, currentlength, currentdepth - 1)
        turtle.left(60)

        turtle.pencolor('red')
        koch_segment(turtle, currentlength, currentdepth - 1)
        turtle.right(120)

        turtle.pencolor('green')
        koch_segment(turtle, currentlength, currentdepth - 1)
        turtle.left(60)

        turtle.pencolor('orange')
        koch_segment(turtle, currentlength, currentdepth - 1)

screen = Screen()
wx = screen.window_width()/2
wh = screen.window_height()/2

base_length = wh * 2 / 3.0**0.5  # the base length is dependent on the screen size

turtle = Turtle()
turtle.fillcolor('grey')  # some color we haven't used as a pen color
turtle.shape('turtle')
turtle.speed('fastest')

turtle.penup()
turtle.setposition(-wx/2, -wh/2)  # start in the lower left quadrant middle point
turtle.pendown()
turtle.left(60)

turtle.begin_fill()
koch_segment(turtle, LENGTH, DEPTH)
turtle.end_fill()

screen.exitonclick()

I've made slight changes to your program, like counting down on the recursion depth instead of up, to make it simpler for me to work with.