Port Saint Lucie
Ok, at the beginning of the game your get 1 card of each colour to start. While I've searched for a similar answer, I believe that yes you will always have 4 needs cards in your hands (one of each color) at the end of a round.
My Questions are do you always have 4 cards in your hand at the end of the "Needs" phase?
What if you have more due to a potion or Magic book?
Do you have to discard down to 4 or will you keep the extras for the next "Needs" phase?
If you have more due to a potion, discard one of the extra colors of your choice back down to your initial hand.
If you have a Magic Book, however that allows you to have +1 card per book you have (currently the color you choose, I tell the players to point toward the board, that way we know what extra color they will have per turn.)
You should be back down to 4 cards (one of every color) unless you have the books that allow more cards.