In the 11th Doctor episode The Big Bang, the Doctor sets up the ending by telling Amy:
A daft old man who stole a magic box and ran away. Did I ever tell you that I stole it? Well, I borrowed it. I was always going to take it back. Oh, that box, Amy. You'll dream about that box. It'll never leave you. Big and little at the same time. Brand new and ancient. And the bluest blue ever.
The setup here is obviously for the wedding custom of 'something old, something new, something borrowed, something blue' (unfortunately, like most modern takes, missing the "and a silver sixpence in her shoe"). The Doctor has always maintained that he "borrowed" the TARDIS, so that fits, and it's clearly both blue and old.
I don't really understand how the TARDIS can be considered "new". It's at least at old as he is (debatable, but at least 900). It had a refresh of the interior with the introduction of the 11th Doctor (as is usual with a reincarnation), but that was an entire season earlier, so it seems doubly a stretch to call it new.