rimTint property
How far the isotropic rim (rimMix) turns from white towards rimHue (0 = white, the default; iOS 26's tab lens has a teal rim). Negative splits the rim's colour by side instead, by this much: with rimHue 180, cooler where the outline faces left and warmer where it faces right (iOS 26's dark tab lens); with 0, the reverse (its light lens).
Implementation
final double rimTint;