Do you know the importance of color contrast？

What is Color Contrast?

Objects don’t inherently possess color—color is produced through the reflection of light wavelengths. When you perceive color, your eyes receive and process these wavelengths, converting them into the colors we see.

Color contrast refers to the difference in luminance between two colors. This difference enables us to perceive color distinctions. Through color contrast, we can emphasize the characteristics and personality of colors. Contrast determines both the brightness level and visual impact of colors.

High contrast means colors are distinctly different, making images more eye-catching, while low contrast creates a softer, more harmonious appearance. Color contrast finds extensive applications in visual design, accessibility, and image processing.

In digital accessibility discussions, color is often analyzed through Hue, Saturation, and Lightness (HSL). The HSL model serves as an alternative to the RGB color model, better aligning with human color perception.

Meanwhile, OKLCH (based on perceptual uniformity) provides even more accurate representation of human color perception, making it ideal for high-precision color control.

Understanding WCAG

According to the World Health Organization’s (WHO) 2021 report, approximately 253 million people

worldwide experience vision impairment. These visual challenges may include myopia, hyperopia, astigmatism, and other eye conditions. The definition of vision impairment typically includes individuals with visual acuity below 20/60, who may face difficulties in daily life.

To support people with various visual impairments, the WAI team developed the color contrast formula, ensuring text maintains sufficient contrast against its background. By adhering to these contrast ratios, users with moderate vision impairment can read text without requiring contrast-enhancing assistive technologies.

• WCAG

(Web Content Accessibility Guidelines) is a series of standards published by the Web Accessibility Initiative (WAI) of the World Wide Web Consortium (W3C). These guidelines help designers and developers create web content that’s more accessible to people with disabilities. While not legally mandatory, WCAG is widely recognized as the international standard and best practice for web accessibility.

At its core, WCAG establishes testable success criteria to ensure people with disabilities can perceive, operate, understand, and effectively interact with web content.

Key WCAG Principles:

• Perceivable Ensure content can be perceived through multiple senses (visual, auditory, or tactile)
• Operable Ensure users can interact through various methods (keyboard, mouse, voice input, etc.)
• Understandable Ensure content is clear and easy to comprehend
• Robust Ensure content functions across different user agents and technologies

Each principle contains multiple guidelines, further divided into testable success criteria with three conformance levels (A, AA, AAA).

While many usability principles mention readability, how should designers actually implement it? Though individual designers may have different approaches, we need scientifically validated standards to evaluate color contrast readability.

WCAG provides specific color contrast requirements.

Color contrast measures the difference in luminance or light intensity between two colors, ranging from 1:1 to 21:1 (pure black vs. pure white). Higher ratios indicate greater relative brightness between colors.

To accommodate different scenarios, WCAG establishes two contrast standards: Minimum Contrast (Level AA) and Enhanced Contrast (Level AAA).

• 1. Level AA Requirements:
• Regular text and text images: minimum 4.5:1 contrast ratio
• Large text (bold 14pt/regular 18pt+) and large text images: minimum 3:1 ratio
• 2. Level AAA Requirements (more stringent):
• Regular text and text images: minimum 7:1 contrast ratio
• Large text (bold 14pt/regular 18pt+) and large text images: minimum 4.5:1 ratio

Both Material Design and iOS Human Interface Guidelines primarily follow Level AA standards, with Level AAA reserved for special cases.

Beyond text-background contrast, designers should also ensure graphical elements meet at least Level AA standards. In dark mode, avoid excessively saturated colors—all surfaces should maintain at least 4.5:1 contrast (Level AA). High-saturation colors on dark backgrounds may cause optical vibration, leading to eye strain.

Color Contrast Testing Tools

Research shows hue and saturation have minimal impact on readability—the true factor affecting reading experience is luminance contrast. While WCAG’s contrast formula is based on relative luminance, designers don’t need complex calculations thanks to modern web tools:

Contrast Grid

Site: Contrast Grid

Figma Color Contrast Checker

Site: Figma Color Contrast Checker

Adobe Color

Site: Color Contrast Checker

WebAIM’s Color Contrast Checker

Site: WebAIM’s Color Contrast Checkerr

These tools make color selection easier by quickly calculating and displaying contrast in real time, and even assisting you in generating the right color match.

Conclusion

Design trends are in full swing every year, and we may occasionally break the mold when working with colors in search of a more stylized, stronger design, or a bolder design. But please don’t forget that maintaining clarity is an important principle in UX design, which enhances the readability of the interface, facilitates better communication of information to users, and improves the user experience.

This is very important in design, so at your leisure, you can also use the tool above to test whether the contrast meets the WCAG standard.