The color seems to be ?androidprv:attr/materialColorSurfaceBright which is a private system color.
?androidprv:attr/materialColorSurfaceBright
But I just found out that the color is equivalent to MaterialTheme.colorScheme.surfaceContainer of androidx.compose.material3.MaterialTheme.
MaterialTheme.colorScheme.surfaceContainer
androidx.compose.material3.MaterialTheme