I am black when you buy me Red when you use me And white when you throw me away What am I?

I wait in jars or boxes tight, a golden round of pure pastry delight. You swore you’d have just one, then stop, but now the sleeve is at the top.

If you hate me, you may hate yourself, but even with infrequent meetings I know your face well. A most impartial judge, watch as I see around corners. On a dark day, I might be cloaked by mourners.

Consumable, not edible, I disappear to disappear At best, I leave no trace behind, at worst, I leave a smear I'm larger when I'm on my own, but still fit in your hand Or small when perched upon an end, and held by metal band

I start with T, I end with T, and I hold T within.