Named colors and hex codes in Matplotlib - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a named color in matplotlib?

A named color is a color identified by a simple name like 'red', 'blue', or 'green' that matplotlib recognizes and can use directly in plots.

beginner

What does a hex code represent in color specification?

A hex code is a 6-digit code starting with '#' that represents a color by specifying the amounts of red, green, and blue in hexadecimal format, like '#FF0000' for red.

beginner

How do you use a named color in a matplotlib plot?

You can use a named color by passing its name as a string to color-related parameters, for example: plt.plot(x, y, color='blue').

beginner

Give an example of a hex code for the color green.

The hex code for green is '#00FF00'. It means no red, full green, and no blue.

intermediate

Why might you choose a hex code over a named color in matplotlib?

Hex codes allow you to specify exact shades and more colors than the limited named colors, giving you more control over the plot's appearance.

Which of these is a valid named color in matplotlib?

A skyblue

B #12345G

C bluish

D reddish

Only 'skyblue' is a valid named color. Hex codes must have valid hex digits, and 'bluish' and 'reddish' are not recognized named colors.

What does the hex code '#0000FF' represent?

A Blue

B Red

C Green

D Black

The hex code '#0000FF' means no red, no green, and full blue, so it represents blue.

How would you specify the color red using a named color in matplotlib?

A #00FF00

B #FF0000

C red

D blue

The named color for red is simply 'red'. Hex codes like '#FF0000' also represent red but are not named colors.

Which is true about hex codes in matplotlib?

A They are only used for grayscale colors

B They use decimal numbers

C They always start with '@'

D They start with '#' and use hexadecimal digits

Hex codes start with '#' and use hexadecimal digits (0-9, A-F) to represent colors.

Why use named colors instead of hex codes?

A Hex codes are not supported in matplotlib

B Named colors are easier to remember and type

C Named colors allow more precise color control

D Named colors are faster to render

Named colors are easier to remember and type, making them convenient for quick plotting.

Explain the difference between named colors and hex codes in matplotlib.

Think about how you pick colors for clothes versus mixing paint exactly.

How would you use a hex code to set a plot line color in matplotlib? Give an example.

Remember the syntax plt.plot(x, y, color='...')

Practice

1. Which of the following is a valid named color in matplotlib?

easy

A. #12345G

B. bluish

C. red

D. 123456

Solution

1. Step 1: Understand named colors in matplotlib

   Matplotlib supports standard color names like 'red', 'blue', 'green', etc.

2. Step 2: Check each option

   red is 'red', a valid named color. #12345G has an invalid hex code with 'G'. bluish 'bluish' is not a recognized name. 123456 is just digits, not a named color.

3. Final Answer:

   red -> Option C

4. Quick Check:

   Named color 'red' is valid [OK]

Hint: Named colors are simple words like 'red' or 'blue' [OK]

Common Mistakes:

• Confusing invalid hex codes as named colors
• Assuming any color-like word is valid
• Using numbers without '#' as colors

2. Which of the following is the correct way to specify a hex color code in matplotlib?

easy

A. "#1a2b3c"

B. "1a2b3c"

C. "#12345"

D. "#xyz123"

Solution

1. Step 1: Recall hex color code format

   Hex codes start with '#' followed by exactly 6 hexadecimal digits (0-9, a-f).

2. Step 2: Validate each option

   "#1a2b3c" has '#' and 6 valid hex digits. "1a2b3c" misses '#'. "#12345" has only 5 digits. "#xyz123" contains invalid letters 'x' and 'z'.

3. Final Answer:

   "#1a2b3c" -> Option A

4. Quick Check:

   Hex code must start with '#' and have 6 hex digits [OK]

Hint: Hex codes start with '#' and have 6 hex digits [OK]

Common Mistakes:

• Omitting the '#' symbol
• Using wrong number of digits
• Including invalid characters

3. What color will the following matplotlib code produce?

import matplotlib.pyplot as plt
plt.plot([1, 2, 3], color="#00FF00")
plt.show()

medium

A. Black

B. Blue

C. Red

D. Green

Solution

1. Step 1: Understand the hex code used

   "#00FF00" is a hex code where red=00, green=FF, blue=00, meaning full green.

2. Step 2: Match hex code to color

   Since green is max and others zero, the line color will be bright green.

3. Final Answer:

   Green -> Option D

4. Quick Check:

   "#00FF00" means green color [OK]

Hint: Hex #00FF00 means full green, no red or blue [OK]

Common Mistakes:

• Confusing hex digits order
• Assuming #00FF00 is blue
• Ignoring case sensitivity in hex

4. Identify the error in this matplotlib color specification:

plt.plot([1, 2, 3], color="#123ABZ")

medium

A. Missing '#' in hex code

B. Invalid hex code due to 'Z'

C. Color name not recognized

D. Syntax error in plot function

Solution

1. Step 1: Check hex code characters

   Hex codes only allow digits 0-9 and letters A-F (case insensitive). 'Z' is invalid.

2. Step 2: Confirm error type

   The code has '#' and correct length, but 'Z' makes it invalid hex code.

3. Final Answer:

   Invalid hex code due to 'Z' -> Option B

4. Quick Check:

   Hex digits must be 0-9 or A-F only [OK]

Hint: Hex codes only use digits 0-9 and letters A-F [OK]

Common Mistakes:

• Ignoring invalid characters in hex
• Confusing missing '#' with invalid chars
• Assuming any letter is allowed in hex

5. You want to plot two lines in matplotlib: one red and one with a custom color #FF8800. Which code snippet correctly sets these colors?

hard

A. plt.plot(x, y1, color='red')
plt.plot(x, y2, color='#FF8800')

B. plt.plot(x, y1, color='#red')
plt.plot(x, y2, color='FF8800')

C. plt.plot(x, y1, color='ff8800')
plt.plot(x, y2, color='red')

D. plt.plot(x, y1, color='red')
plt.plot(x, y2, color='FF8800')

Solution

1. Step 1: Check named color usage

   Named colors like 'red' are used as strings without '#'. Adding '#' to named colors makes them invalid.

2. Step 2: Check hex code usage

   Hex codes must start with '#'. Omitting '#' for hex colors like 'FF8800' or using lowercase without '#' is invalid.

3. Final Answer:

   plt.plot(x, y1, color='red') plt.plot(x, y2, color='#FF8800') -> Option A

4. Quick Check:

   Named colors no '#', hex codes start with '#' [OK]

Hint: Named colors no '#'; hex codes start with '#' [OK]

Common Mistakes:

• Adding '#' to named colors
• Omitting '#' in hex codes
• Using lowercase hex without '#'