Error rgb()/rgba() color channel out of range

Example

/* Wrong: 300 is above the 0-255 range */
.banner { background: rgb(300, 0, 0); }

/* Wrong: alpha above 1 */
.banner { background: rgba(0, 0, 0, 1.5); }

/* Right */
.banner { background: rgb(255, 0, 0); }
.banner { background: rgba(0, 0, 0, 0.5); }

Why it matters

Each of red, green, and blue represents one byte of color intensity, which is exactly why the valid range tops out at 255 — it's the largest value a single byte can hold. A value like 300 isn't a "very saturated" red; it's simply outside the format entirely. Browsers handle this by clamping the out-of-range value down to the nearest valid one (300 becomes 255), so the color often still renders — just not distinguishably different from what plain 255 would have produced, which masks the mistake. This usually comes from a manual typo, or from color values calculated programmatically (a lightening/darkening function, for instance) without clamping the result to the valid range before writing it out.