Adjust color alpha
Set transparency explicitly without mutating the source color.
Transparent
alpha 0
#7c3aed00
Translucent
alpha 0.45
#7c3aed73
Opaque
alpha 1
#7c3aedff
Change transparency, not color channels
The RGB channels remain 124, 58, and 237. Only alpha changes, and eight-digit hex quantizes 0.45 to 0x73.
Set alpha on an immutable color
withAlpha() returns the same concrete color type with a clamped alpha value. The original object remains opaque.
<?php
use PhpColor\Color\Color;
$source = Color::parse('#7c3aed');
$translucent = $source->withAlpha(0.45);
printf("%s\n%s\n",
$translucent->toCss(),
$translucent->toHex(withAlpha: true),
);
// rgb(124 58 237 / 0.45)
// #7c3aed73Choose the representation at the boundary
Alpha is stored from 0 to 1. Serialization decides how that value is rounded for CSS or storage.
CSS alphatoCss() keeps the decimal alpha value visible.
Hex alphatoHex(true) writes a quantized eighth channel pair.
ClampingValues below 0 become 0; values above 1 become 1.
No compositingChanging alpha does not resolve the color against a background.