Flutter : how to change theme color of button in floating action button?

1. Question background

I want to change the background color of button, keeping the original color of icon. In my program, my button color is blue. Since I wanted to remove the blue color, I tried several ways. But everything didn't work.

2. What I already tried

1. theme : ThemeData

   theme: ThemeData( colorScheme: const ColorScheme.light( primary : Colors.lime, ), ),

2. backgroundColor : Theme.of()

   backgroundColor: Theme.of(context).primaryColor,

(etc using theme color modification)

3. My code and Result

      body : Center(
        child: Container(
          height: 500,
          color: Colors.lime[200],
          child: ListView.builder(
            itemCount :name.length,
            itemBuilder: (c,i){
              return Align(
                alignment: Alignment.bottomRight,
                child: ListTile(
                 leading: const Icon(Icons.shopping_bag),
                  title : Text(name[i]),
                ),
              );
            },
          ),
        ),
      ),

      floatingActionButton: FloatingActionButton(
        theme: ThemeData(
          colorScheme: const ColorScheme.light(
            primary : Colors.lime,
          ),
        ),
        onPressed: (){
          showDialog(context: context, builder: (context) {
            //designate the developer made function into specific name
            return DialogUI(usingaddOne:addOne, usingaddString : addString);
          });
        },
        child : const Icon(Icons.shopping_cart, ,),
      ),
    );}
}

Result

4. Question

I want to change the button with lime (or red) background color with the original color of icon. Or just remove the blue color. Is there any other way that i've not tried?

You are doing it right, just in the theme there is an attribute like this :

static ThemeData get lightTheme {
    return ThemeData(
      primarySwatch: Colors.white, // your main color app
      brightness: Brightness.light,
      fontFamily: 'Segoe',

      // * FLOATING ACTION BUTTON THEME
      floatingActionButtonTheme: FloatingActionButtonThemeData(
        elevation: 2, // elevation
        backgroundColor: Colors.lime, // the background color
      ),
    );
  }
}

This static ThemeData variable (create it in other class, i named AppTheme), you can write it in your main.dart in the MaterialApp like this :

 return MaterialApp(
    debugShowCheckedModeBanner: false,
    title: 'Flutter Demo',
    theme: AppTheme.lightTheme, // here
    initialRoute: PageNames.home,
 );

And in your FloatingActionButton, you don't have to do any other thing

 FloatingActionButton(
    onPressed: () => onAction(),
    child: Icon(
       Icons.add,
       color: Colors.white,
    ),
 ),

In other words, delete the theme in your FloatingActionButton Widget and put it in your MaterialApp