Feedback Messages best practice

Currently i am working on Feedback messages for an ecommerce website in different state and i am looking for best practice regarding the

  • Feedback message/notification color ?
  • should be with icon or not?
  • for how long the feedback/notification message should stay?
  • do i need to give the user the ability to remove the error message by providing (x) button inside the feedback message/notification

it would be great if you can provide some examples :

I like MailChop feedback messages:

http://ux.mailchimp.com/patterns/feedback