The MTR (Tournament Rules) indicate that you are not supposed to reveal the contents of your booster (which includes your pick); visually or otherwise. You may, however, reveal double-faced cards.
7.7 Booster Draft Procedures
Players may not reveal the front face of their card selections or the contents of their current packs to other participants in the draft and must make a reasonable effort to keep that information from the sight of other players. Players are not permitted to reveal hidden information of any kind to other participants in the draft regarding their own picks or what they want others to pick. (Exception: This does not apply to double-faced cards, both faces of which may be revealed at any time during a draft.)
The Tournament Rules can be found here: https://wpn.wizards.com/en/rules-documents
An alternative source that provides comments from/for judges is the Judge rules resources: https://blogs.magicjudges.org/rules/mtr7-7/
As for whether revealing your favorite cards before the draft is permissible: The rules don't explicitly disallow it, and of course chatting about your favorite colors for decks before a match shouldn't be a problem. If I try really hard, I can think of scenarios where this might fall into collusion or unsporting conduct territory, but you would certainly have to get there intentionally.