Color theory, often discussed in articles and books, might not always be the key to making great UI designs. Instead, the author believes in the power of color modifications, emphasizing the importance of tweaking a base color into various shades and variations. Here's a condensed breakdown of the insights shared:

Key Takeaways:

1. Darker & Lighter Variations: Many well-designed interfaces feature darker and lighter variations of a primary theme color.
2. Real-World Reference: In reality, shadows provide an example of how colors change. A shadow is essentially a darker variation of a base color.
3. HSB Color System: Colors are best understood and modified using the Hue, Saturation, and Brightness (HSB) system.
4. Rules for Color Variations:
• Darker variation: Lower the brightness and increase saturation.
• Lighter variation: Increase brightness and decrease saturation.
5. Hue's Role: Hue, or the specific type of color, can be secondary when making color adjustments. However, hues have a perceived brightness or "luminosity." Adjusting hues towards red, green, or blue makes colors appear darker, while adjusting towards yellow, cyan, or magenta makes them appear brighter.
6. Using One Base Color: It's possible to design an entire interface using one base color by making necessary modifications based on the principles discussed.

In essence, effective color usage in UI design doesn't always require an elaborate palette. Mastery over modifying a single color and understanding its different variations can be more pivotal.

Building a Useful Color Palette

1. Common Misconception: Automated color palette generators give you about five colors, but this approach isn't always practical for designing a real-world website.
2. Three Main Color Categories:
• Greys: Used in most interface elements, like text and backgrounds. You'll likely need 8-10 different shades, from a deep grey (not pure black) up to white.
• Primary Colors: One or two main colors representing your site (e.g., Facebook's blue). Requires 5-10 shades ranging from light to dark.
• Accent Colors: Supplementary colors to communicate specific actions or states, like warnings or highlights. Depending on the complexity, you might need up to 10 different colors with 5-10 shades each.
3. Building Your Palette:
• Start with a Base Color: Choose a neutral color that could be used for a button background.
• Find the Extremes: Decide on your darkest and lightest shades for each color category.
• Fill in the Middle: After choosing your darkest, lightest, and base shades, fill in the in-between shades. A 9-shade system (labeling the darkest as 900 and the lightest as 100) can be balanced and versatile.
4. Tips:
• Avoid using CSS functions to lighten or darken colors on-the-go; it leads to inconsistency.
• Trust your judgment. While the systematic approach is a good starting point, fine-tuning with your eyes is essential.
• Limit the number of shades to maintain a coherent design.

WCAG and Its Importance in UI Design

1. Introduction to WCAG:
• The Web Content Accessibility Guidelines (WCAG) set rules to make products accessible to those with disabilities.
• Developed as an open standard by W3C, they're not exhaustive but serve as a general framework.
2. Relevance of WCAG 2.1:
• Recognized as the primary standard for accessibility.
• Legally required by many governments via laws like Section 508 and the European Accessibility Act (EAA).
• Essential for those selling to government organizations.
• Enhances user experience for a broader audience, factoring in temporary disabilities.
3. Levels of Conformance:
• Three levels: A, AA, and AAA.
• Most aim for AA as it balances accessibility with brand design.
• AAA is extensive, e.g., it requires a 7:1 contrast ratio for text.
4. WCAG 2.1 and Color Contrast:
• Designers frequently address color contrast requirements.
• Contrast ratio measures the difference in luminance between two colors.
• W3C focuses on luminance contrast as it is perceivable by nearly everyone.
5. Understanding Contrast Ratios:
• Defined by the difference in brightness between two colors.
• Several tools available for designers to check contrasts, e.g., WebAIM Contrast Checker.
6. Contrast Requirements:
• Text should have a 4.5:1 contrast ratio with the background.
• Links need a 3:1 contrast if they don’t have another visual cue.
• UI components should have a 3:1 contrast ratio with their surroundings.
• Focus indicators should have specific contrast levels and dimensions.
7. Interaction States:
• No specific requirements for hover states, but the text must maintain a 4.5:1 contrast ratio.
8. Conclusion:
• WCAG 2.1 is vital for accessibility and broadening product reach.
• AA conformance strikes a balance between accessibility and design.
• Accessibility benefits not just those with permanent disabilities but also those with temporary impediments.