What the tile is painted — bg-indigo-600.
OptionalfgWhat the glyph inherits — text-gray-900.
Omit on a dark tile, where --color-on-surface from Launcher is already right. State
it on a light one: Notes on bg-yellow-400 inherited a near-white glyph at 1.19:1, and
nothing in a single string could say whether that was a decision or an omission.
A launcher tile, as two named roles rather than one string with two jobs in it.
Both are utility classes from
app-utilities.css, not colour values —AppIconinterpolates them into aclassattribute, so a hex string is a class name matching no rule and the tile renders with no background at all. That used to be a DEV-onlyconsole.warn, which is the weakest gate in the repo;defineAppthrows on it now.