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Color output (alpha, hex, gamut)

Un-operated color literals follow the verbatim rule. The rules here govern colors Jess actually computes, plus one preservation rule for authored alpha-hex.

Computed alpha → rgba(...)​

When a color operation produces an alpha below 1, the result serializes in rgba(...) legacy syntax (the modern rgb(r g b / a) form is used only when the source color was authored in modern syntax):

.a { color: fade(#e04141, 50%); }
.a { color: rgba(224, 65, 65, 0.5); }

Alpha-hex literals are preserved as hex​

An authored alpha-hex literal — 4-digit #rgba or 8-digit #rrggbbaa — stays in hex form when nothing operates on it, rather than being rewritten to rgba(...):

.a {
  color: #ff000080;
  background: #f003;
}
.a {
  color: #ff000080;
  background: #f003;
}

Only a computed alpha-hex color canonicalizes — and then, with alpha < 1, it follows the rgba(...) rule above.

Out-of-gamut channels clamp​

A computed color whose channels fall outside their valid range is clamped — rgb channels to 0–255, saturation/lightness to 0–100%, alpha to 0–1:

.a { color: lighten(#800000, 100%); }   // lightness past 100% -> clamps to white
.a { color: #ffffff; }

This is the same color model as the Less 5.x engine — see the Less Color Output page.