The categories are:
Cost / Expansion / Handsize / Actions / Buys and Gains
Cost needs to be exact, and orange may be given if you only get the right number value (could affect Potion, Debt, even * or +).
Expansion is obvious (though specific to 1st or 2nd Ed could result in orange).
Handsize is after play from a normal starting hand of 5 cards. If there are multiple possible handsizes, and you only match some, it will be orange.
Actions is a simplification of the 4th category... basically, the ability to play another card in the current phase (e.g. a Treasure, Night, or Throne Room all allow you to play another card, similar to +1 Action, so any of these would be orange if another of them were correct).
Buys and Gains is the ability to get an extra card on that turn.
I'm thinking of a card, selected pseudo-randomly. Guess away.