Uses of ThemeData.accentColor should be replaced with
ThemeData.colorScheme.secondary.

Migration guide

Code before migration:

var

myTheme

ThemeData

//...

accentColor:

Colors

blue

//...

);

var

color

myTheme

accentColor

Code after migration:

var

myTheme

ThemeData

//...

colorScheme:

ColorScheme

//...

secondary:

Colors

blue

//...

),

//...

);

var

color