[jQuery] How do you iterate across elements with the same class name?

[Thierry]

I have a bunch of hyperlinks with class 'hello_world'.  I want to
assign each one of them a random colour.  I can set the colour for all
of them with the following:

$("a[class=hello_world]").css("color", "red");

How can I iterate over every element with class name 'hello_world'?