tinyletter is a free email marketing service (to send newsletters) that has been acquired and is developed now by more popular MailChimp.
It does not have all complexity that MailChimp has, but offers you the basic tools to create a signup form, compose emails, import lists with subscribers from CSV file or Gmail and send them newsletters for free.
Can customize background color or use an image, choose between different font types, set desired colors for any part of form. Also, customize emails for new subscribers or unsubscribers.
If you are new to email marketing and you want a free solution with all basic options included, tinyletter is good for that.