Color Vision Lab is a free, open-source, private and offline app for colour vision screening and everyday colour tools, built with Tauri v2, React and Rust for Windows, macOS, Linux, Android, iOS and the web. Users can take quick (7-plate) or full (16-plate) Ishihara-style screening, where plates are generated fresh from Machado confusion lines with lightness noise so they cannot be memorised; a D-15 hue arrangement scored with the Vingrys & King-Smith method (C-index, S-index, axis angle, crossings); and an adaptive contrast sensitivity test that reports log CS. A results report shows type, severity, confidence and a per-plate breakdown and exports to printable HTML. The Color Lens names the colour under the crosshair from the live camera or a photo, with protan/deutan/tritan simulation or enhancement, freeze frame and spoken names, and the photo simulator shows all three types side by side with a daltonize mode, processing pixels in Rust in the app and TypeScript on the web. History has trend charts, CSV export and JSON backup, and a 60-second odd-hue game builds a daily streak. It supports English, Bangla, Spanish and Hindi, high contrast, reduced motion, screen readers and full keyboard use. Desktop builds get signed auto-updates from GitHub Releases and deep links. Version 3.0 rebuilt the earlier Kotlin/Compose Android app. It is a screening aid, not a diagnosis. MIT licensed.