Players may rearrange their hand cards and change their orientation to help themselves remember the information they received. Players may not ever look at the front of their own cards until the play them.
The discard pile may always be searched for information.
Hanabi based on communication and non-communication between the Players. If one interprets the rules strictly then players may not, except for the announcements of the current player, talk to each other.
Ultimately, each group should decide by its own measure what communication is permitted communication. Play so that you have fun!
If a player discards a card about which they have not received a clue, they run the risk of discarding from the game a card that might be needed to complete a firework.
Sometimes a player will have no choice but to discard a card about which they know nothing. If that happens, remember that there are multiple copies of each card, so a discard will not necessarily condemn a firework.
Clearly identify a firework when you know that it can't be finished. You will then always know that card of that color can safely be discarded to return blue counters to the tin lid.