Flutter – Errors in this repository

I was taking a course which had old version of Flutter SDk which showed errors at main.dart files which I was able to eliminate by changing the dependencies in the .yaml file. But The file names color turned red when I did that change. Is it a problem or its just that way?

One other issue is again with the .yaml file where I cannot understand why it shows error when i use asset image from the folder. I followed exactly how the course instructed but the image is thrown everytime.
This is the code from the .yaml file

flutter:
  uses-material-design: true
  assets:
    - Images/diamond.png

and this is the code from the main file.

void main() {
  runApp(MaterialApp(
    home: Scaffold(
      backgroundColor: Colors.blueGrey,
      appBar: AppBar(
        backgroundColor: Colors.blueGrey[900],
        title: const Center(child: Text('I am rich')),
      ),
      body: const Center(
        child: Image(image: AssetImage('Images/diamond.png')),
      ),
    ),
  ));
}