pub fn derive_ink(hex: &str) -> AccentInkExpand description
Pick an AAA-safe text color to pair with an accent fill.
Uses the classic YIQ luminance formula. Threshold 160 was chosen against the standard Wave Funk pastel palette and a fixture of 20 accents: it keeps every pastel above the line (black text) and every saturated deep color below (white text). Invalid hex falls back to white ink — safest for an accent we can’t reason about.