onSurface property
A color that is clearly legible when drawn on surface color.
To ensure that an app is accessible, a contrast ratio of 4.5:1 for surface and onSurface is recommended. See www.w3.org/TR/UNDERSTANDING-WCAG20/visual-audio-contrast-contrast.html.
If null, the on color is derived from the brightness of the surface color, and will be be black if it is light and white if it is dark.
Implementation
final Color? onSurface;