i can't understand ....anything

public void Circle() {
        color = new Color();
    }

Remove the "void". Since we need to return information from the object, the void must be removed.

public Circle() {
        color = new Color();
    }

public void Circle() - Constructor function returns the object it creates and not void. So Avoid .......

in the hint, it mentions to study the default constructor, when you check the default constructor, just review the differences between regular methods and constructors, hopefully you will figure out the answer