Designers hand off hex strings. Developers paste them. And three times out of ten the string is fine and the render is still wrong — because a hex value is not a color, it's a set of numbers that each platform reads differently.

1. Eight digits, two different channel orders

CSS defines 8-digit hex as #RRGGBBAA — alpha last. Android, Flutter and Kotlin define it as #AARRGGBB — alpha first. So #80FF0000 is:

CSS: red 0x80 , green 0xFF , blue 0x00 , alpha 0x00 → completely invisible. Your UI element quietly disappears.

Android: alpha 0x80 , red 0xFF , green 0x00 , blue 0x00 → a 50% red overlay.

Same literal, opposite meaning, no error anywhere. Six-digit hex is safe because all three channels are present in the same order; the moment you add the fourth pair you have an ambiguous string. Hand off rgba(255, 0, 0, 0.5) or a 6-digit hex plus a separate opacity token instead.

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