The color to use when drawing the icon.
Defaults to the current IconTheme color, if any.
The color (whether specified explicitly here or obtained from the
IconTheme) will be further adjusted by the opacity of the current
IconTheme, if any.
In material apps, if there is a Theme without any IconThemes
specified, icon colors default to white if the theme is dark
and black if the theme is light.
If no IconTheme and no Theme is specified, icons will default to
See Theme to set the current theme and ThemeData.brightness
for setting the current theme's brightness.
Typically, a Material Design color will be used, as follows:
final Color? color;