C# does not exist in the current context

public void DoStuff()
{
    List<Label> RpmList = new List<Label>();
    RpmList.Add(label0x0);
    RpmList.Add(label0x1);
    RpmList.Add(label0x2);
    RpmList[0].BackColor =开发者_StackOverflow中文版 System.Drawing.Color.Yellow;
}

public void Form1_Load(object sender, EventArgs e)
{
    DoStuff();
    RpmList[1].BackColor = System.Drawing.Color.Yellow;    //    <---THIS ONE
}

How can I access the list inside DoStuff() method from all my other classes?

Inside DoStuff() method I access Form1 labels.

You should read about variable scope

Return the list from the method and assign it to a local variable, then use the local variable.

 private List<Label> DoSomething()
 {
     ...
     return RpmList;
 }


 ...
 var list = DoSomething();
 list[0].BackColor = ...

First of all method names can be other then that.

Second, declare RpmList like this:

class ClassName
{
 List<Label> RpmList = new List<Label>();

 public void DoStuff()
 {
    RpmList.Add(label0x0);
    RpmList.Add(label0x1);
    RpmList.Add(label0x2);
    RpmList[0].BackColor = System.Drawing.Color.Yellow;
 }

}

Your RpmList variable is private to the DoStuff method. You need to move it out the method which makes it a global variable and therefore has scope to the entire class. I would recommend reading up about Object Oriented Programming because you are offending a very basic law to the whole methodology (encapsulation and variable scope). Anyway, to resolve your problem:

List<Label> RpmList = new List<Label>();

public void DoStuff()
{    
    RpmList.Add(label0x0);
    RpmList.Add(label0x1);
    RpmList.Add(label0x2);
    RpmList[0].BackColor = System.Drawing.Color.Yellow;
}

public void Form1_Load(object sender, EventArgs e)
{
    DoStuff();
    RpmList[1].BackColor = System.Drawing.Color.Yellow;    //    <---THIS ONE
}