Hex colors in CSS - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Hex Color Codes

What color will the CSS rule color: #FF0000; produce when applied to text?

A Black

B Bright green

C Bright red

D Bright blue

💡 Hint

The first two digits in a hex color code represent the red component.

The hex color #FF0000 means full red (FF), no green (00), and no blue (00), so the color is bright red.

📝 Syntax

intermediate

Valid Hex Color Syntax

Which of the following CSS hex color codes is invalid and will cause the browser to ignore the color?

A #12G45F

B #FFF

C #123ABC

D #000000

💡 Hint

Hex digits can only be 0-9 and A-F.

Option A contains the letter 'G', which is not a valid hex digit. Valid hex digits are 0-9 and A-F.

❓ rendering

advanced

Visual Result of Short Hex Color

What color will the CSS rule background-color: #0F0; produce on a webpage?

A Bright red

B Bright green

C Bright blue

D Dark gray

💡 Hint

Short hex colors repeat each digit to form the full 6-digit code.

The short hex #0F0 expands to #00FF00, which is bright green.

❓ selector

advanced

CSS Selector and Hex Color Application

Given the CSS rule p.highlight { color: #800080; }, what color will the text inside a paragraph with class highlight be?

CSS

<p class="highlight">Sample text</p>

A Purple

B Orange

C Teal

D Yellow

💡 Hint

The hex code #800080 is a common purple color.

The hex color #800080 is a shade of purple, so the text will appear purple.

❓ accessibility

expert

Hex Color Contrast for Accessibility

Which hex color combination provides the best contrast for text readability on a white background?

A Text color: #FF0000 (bright red)

B Text color: #777777 (medium gray)

C Text color: #CCCCCC (light gray)

D Text color: #000000 (black)

💡 Hint

High contrast means very different brightness between text and background.

Black (#000000) on white (#FFFFFF) provides the highest contrast, making text easiest to read for most users.

Practice

1. What does the hex color code #FF0000 represent in CSS?

easy

A. Black color

B. Bright green color

C. Bright red color

D. Bright blue color

Solution

1. Step 1: Understand hex color format

   Hex colors start with # followed by 6 digits: two for red, two for green, two for blue.

2. Step 2: Analyze the code #FF0000

   The first two digits FF mean full red, the next two 00 mean no green, and the last two 00 mean no blue.

3. Final Answer:

   Bright red color -> Option C

4. Quick Check:

   Red = FF, Green = 00, Blue = 00 [OK]

Hint: First two hex digits control red color intensity [OK]

Common Mistakes:

• Confusing red with green or blue
• Ignoring the order of RGB in hex
• Thinking #FF0000 is black

2. Which of the following is the correct syntax for a hex color in CSS?

easy

A. #12345G

B. 123456

C. #XYZ123

D. #1A2B3C

Solution

1. Step 1: Check hex color syntax rules

   A valid hex color starts with # followed by exactly 6 hexadecimal digits (0-9, A-F).

2. Step 2: Validate each option

   #12345G has a 'G' which is invalid. 123456 misses the #. #1A2B3C has valid digits and #. #XYZ123 has invalid letters 'X' and 'Z'.

3. Final Answer:

   #1A2B3C -> Option D

4. Quick Check:

   Valid hex = # + 6 hex digits [OK]

Hint: Hex colors start with # and use digits 0-9, A-F only [OK]

Common Mistakes:

• Using letters outside A-F
• Omitting the # symbol
• Using fewer or more than 6 digits

3. What color will the CSS rule color: #00FF00; display on the webpage?

medium

A. Green

B. Blue

C. Red

D. Yellow

Solution

1. Step 1: Decode the hex color #00FF00

   The first two digits 00 mean no red, the next two FF mean full green, and the last two 00 mean no blue.

2. Step 2: Identify the color from RGB values

   Full green with no red or blue results in bright green color.

3. Final Answer:

   Green -> Option A

4. Quick Check:

   Green = FF, Red & Blue = 00 [OK]

Hint: Middle two hex digits control green color [OK]

Common Mistakes:

• Mixing up red and green positions
• Assuming #00FF00 is blue
• Ignoring hex digit order

4. You wrote background-color: #12345; in your CSS. What is the problem?

medium

A. Hex code is missing one digit

B. Hex code has invalid letters

C. Hex code should start with '0x'

D. Hex code is correct

Solution

1. Step 1: Count digits in the hex code

   The code #12345 has only 5 digits after the #, but hex colors require exactly 6 digits.

2. Step 2: Check other options

   Letters are valid digits (1,2,3,4,5). Hex colors do not start with '0x' in CSS. So the only issue is missing one digit.

3. Final Answer:

   Hex code is missing one digit -> Option A

4. Quick Check:

   Hex colors need 6 digits after # [OK]

Hint: Count digits after #; must be exactly 6 [OK]

Common Mistakes:

• Using 3, 5, or 7 digits instead of 6
• Confusing hex with other number formats
• Thinking '0x' prefix is needed

5. You want a color with equal parts red and blue but no green. Which hex code should you use?

hard

A. #00FFFF

B. #FF00FF

C. #FFFF00

D. #0000FF

Solution

1. Step 1: Understand RGB parts in hex

   Hex colors are #RRGGBB. Equal red and blue means red and blue digits are the same, green digits are zero.

2. Step 2: Check each option

   #FF00FF: #FF00FF has red = FF, green = 00, blue = FF (equal red and blue, no green). #00FFFF has green = FF. #FFFF00 has green = FF. #0000FF has no red.

3. Final Answer:

   #FF00FF -> Option B

4. Quick Check:

   Red = Blue, Green = 00 means magenta [OK]

Hint: Set green digits to 00, red and blue equal [OK]

Common Mistakes:

• Mixing green with blue or red
• Choosing colors with green included
• Not knowing hex digit order