Hi,
Where are you copying the tables from? That might have something to do with the problem you are having. Are you creating the table in Marketo or are you bringing it from outside Marketo by pasting from another application?
If you are using the user interface in Marketo to create the table, the wysiwyg editor will be tricky to do what you are trying. If that is how you are doing it, I recommend that once you have the table that you want to copy, looking the way you want it, then click on the "html" button in the editor. That will show you the actual HTML code that creates the table. Then just select from your table beginning tag to the table ending tags (which are <table... and ...</table>). Once you have copied that, you can paste it within the HTML code wherever you want the new version of the table, and voilá!
I hope that helps.
Oh, and in terms of the border color, that might be a bit tricky if you don't have access to an HTML developer. Not everything that works in a word processor works in HTML. The border is really just the outside when it comes to the HTML configuration you might be using with the Marketo editor (if that is what you are using). There are other ways of creting those effect with more advanced HTML coding, but if your expertise is limited, you might have a hard time making it hapen.
Usually, things like that, at least in emails are better to do them with what I like to call "old-school" HTML. Remember, HTML in an email will not work the same way as in a web page. Only some things do, not everything.
Good luck.
Rafael