Colors, Fill, and Turtle Art

By the end of this lesson you'll be able to:

• Use hex color codes and RGB values to set any color you can imagine
• Explain the difference between the RGB and HSL color models
• Paint solid filled shapes using begin_fill() and end_fill()
• Set both the pen color and background color of the turtle canvas

Colors make turtle art come alive. Until now our turtle has drawn outlines. Today we unlock the full color palette and learn to paint filled shapes.

Welcome to Chapter 12!

Ready to paint? By the end of this lesson your turtle drawings will look like real art. Let's mix some colors and fill some shapes! Let's code it together!

Color in Turtle Graphics

You already know how to set a color by name, like t.pencolor("red"). Python's turtle knows around 140 named colors, from "aquamarine" to "yellow".

But there are millions of colors that don't have names. To reach those, you need color codes.

Hex Color Codes

A hex color code is a six-character code that describes a color precisely. Each code starts with a # sign and contains exactly six letters and numbers.

#FF0000  →  pure red
#00FF00  →  pure green
#0000FF  →  pure blue
#000000  →  black
#FFFFFF  →  white
#FF6347  →  tomato red

The six characters are split into three pairs: - First pair controls red (00 to FF) - Second pair controls green (00 to FF) - Third pair controls blue (00 to FF)

FF means maximum brightness (255 in decimal). 00 means none (0).

What Do You Think Will Happen?

The program below draws a square in three different hex colors. What colors do you think #FF00FF and #FFFF00 will produce? Make your guess — then run it to find out!

import turtle
t = turtle.Turtle()
t.speed(6)
t.pensize(3)

colors = ["#FF0000", "#FF00FF", "#FFFF00"]
positions = [(-150, 0), (0, 0), (150, 0)]

for col, pos in zip(colors, positions):
    t.penup()
    t.goto(pos)
    t.pendown()
    t.pencolor(col)
    for i in range(4):
        t.forward(80)
        t.right(90)

▶ Run ↻ Reset

Were you right? #FF00FF is magenta (red + blue, no green) and #FFFF00 is yellow (red + green, no blue).

The RGB Color Model

The RGB color model mixes red, green, and blue light to make every other color. It's the same model your screen uses — every pixel on your monitor has a tiny red light, a green light, and a blue light.

Color	Red	Green	Blue
Red	255	0	0
Green	0	255	0
Blue	0	0	255
Yellow	255	255	0
Cyan	0	255	255
Magenta	255	0	255
White	255	255	255
Black	0	0	0

You can use RGB values directly in turtle by converting them to a hex color string first. The helper function below does that math so you can keep thinking in 0–255 values.

▶ Run ↻ Reset

Try changing the numbers in the rgb_colors list. Each number goes from 0 (none) to 255 (full brightness).

See It: Mix Your Own Color

What Do You Think Will Happen?

Before you touch the sliders below, predict: to make a bright yellow, which two sliders need to be high, and which one low? Mix it and check the hex code you get!

Explore the RGB Color Mixer MicroSim

Watch the hex code as you drag one slider — only that channel's two digits change, highlighted in yellow. When you find a color you love, copy the t.pencolor(...) line straight into any turtle lab in this chapter. Click New Challenge to play match-the-color.

Background and Pen Colors

Turtle lets you set two separate colors at once.

• t.pencolor("red") — the color of the lines the turtle draws
• t.fillcolor("yellow") — the color used to fill shapes
• turtle.bgcolor("lightblue") — the canvas background color

You can also set both pen and fill at once:

t.color("blue", "yellow")   # pencolor = blue, fillcolor = yellow

Filling Shapes with begin_fill() and end_fill()

To paint a solid shape, wrap your drawing code between two calls:

1. t.begin_fill() — tells the turtle "I'm about to draw a shape to fill"
2. draw the shape
3. t.end_fill() — seals the shape and fills it with the fill color

Before we look at the code, two key points: - You must set the fill color before calling begin_fill() - The shape must be closed (end where it started) for the fill to look correct

import turtle
t = turtle.Turtle()
t.speed(6)

t.fillcolor("gold")
t.begin_fill()
for i in range(6):
    t.forward(100)
    t.right(60)
t.end_fill()

▶ Run ↻ Reset

Try changing "gold" to any color name or hex code. Try changing 6 to 3 for a triangle or 5 for a pentagon.

Color Theory Basics

Before we mix colors on the canvas, let's understand some color theory terms:

• Hue — the basic color family (red, orange, yellow, green, blue, violet)
• Saturation — how vivid or washed-out the color is (100% = vivid, 0% = grey)
• Lightness — how bright or dark the color is (0% = black, 100% = white)
• Complementary colors — colors opposite each other on the color wheel (e.g. red and green, blue and orange). They create strong contrast when placed side by side.

The HSL Color Model

The HSL color model describes colors in three values: Hue, Saturation, and Lightness. Many designers prefer HSL because it's easier to think about than RGB: "I want a moderately bright, slightly greenish blue" is natural in HSL but tricky in RGB.

Python's turtle doesn't support HSL directly, but the concept appears in CSS and image editing tools. You can convert HSL to RGB using the colorsys module (covered later in the course).

Transparency and Alpha

In many drawing systems, color also has an alpha value that controls transparency. An alpha of 1.0 means fully opaque (solid) and 0.0 means fully transparent (invisible).

Python's turtle doesn't support transparency natively, but image processing libraries like Pillow (Chapter 34) do. For now, knowing what alpha means will help you when you encounter it in web design, image editors, and game development.

A Filled Flower

Let's combine everything: fill color, hex codes, and loops to create a colorful flower.

Before the code, note that t.circle(r, extent) draws an arc of a circle. If extent=360 it's a full circle; extent=120 draws one-third of a circle, which we'll use as a "petal."

▶ Run ↻ Reset

Learning Check

Your Turn — Add the Missing Lines

The program below draws a red square outline, but it should be filled with blue. Add the three missing lines — set the fill color, open the fill, and close the fill — to make the square solid blue with a red border!

▶ Run ↻ Reset

Experiments

Try these changes. Predict what will happen first, then run it to check!

1. In the hex color demo, change #FF0000 to #FF8800. You'll know it worked when the first square turns orange.

2. In the RGB circles demo, change the first tuple to (255, 165, 0). You'll know it worked when the first circle turns orange.

3. In the filled hexagon demo, add turtle.bgcolor("navy") before the loop. You'll know it worked when the background turns dark blue.

4. In the filled hexagon demo, add a t.pencolor("#000000") line before t.begin_fill(). You'll know it worked when the hexagon has a black outline around the gold fill.

5. Modify the flower so each petal is the same color but the background is black. You'll know it worked when your single-color flower glows against the dark background.

Beautiful Work!

You've mastered hex codes, RGB, HSL, fill colors, and background colors! Your turtle art is now full-color and full of life. Keep experimenting — every great digital artist started exactly where you are now!

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