Yep, it's red.
But it all depends on how old the actual picture is, and in what sort of lighting Aoyama-sensei drew it in. On the cover of my copies of the first and second volumes (of MK), the tie looks pink, but that's also because it's an old, original copy, and the coloring faded a little. On the third volume, it's red, and on the fourth, you can't see his tie at all. Also, (in my case, it might just be a misprint) but on the thrid volume cover, KID's ribbon on the hat and the shirt underneath the jacket are purple... And then, there are blue spots in his hair on the first, second, and fourth volumes.
It's just like Kaito's Gakuran school jacket. Normally, it's supposed to be black, but on the color pages of the original "Clock Tower" manga chapters, his uniform is colored navy blue because it's night, but there's a tiny bit of lighting.
I think it's probably red, though it does look pretty orange in the movies. It's hard to tell from manga covers because often they tend to alter the colours of outfits to go with a tankoban's cover's colour scheme (Maison Ikkoku and the early volumes of InuYasha did it all the time). But i'd say red.