A Christmas party outfit has one job that's different from every other occasion dress in your life: it has to survive a room where nobody's sitting down for long, the heating is always turned up too high, and you'll be standing near a buffet table at some point holding a drink in one hand and a paper plate in the other. It's not a wedding outfit, where you're performing good behaviour for six hours. It's looser than that, and louder, and it should let you move.
The easiest colours to actually enjoy wearing are the ones that don't need the party to prove themselves, a deep green, a wine red, a bottle black with some texture to it, anything with a bit of shine built into the fabric rather than stuck on top as sequins that scratch your arms by ten o'clock. Metallics in gold or bronze do a lot of work without you trying, and they sit nicely against most skin tones under the sort of orange lighting most offices and pubs decorate with in December. Where it goes wrong is piling too many "party" ideas into one outfit, sequin top with a sequin skirt, velvet with a fur trim with glitter tights, until you've accidentally dressed as a bauble. Pick one loud element and let everything else calm down around it, plain black trousers under a metallic top, a simple slip under a sequin jacket, that sort of balance.
Where this kind of outfit properly falls short is anywhere you'll be sitting through a long meal or standing outside in the cold waiting for a bus, because a lot of party fabrics are built for a warm room and about four hours, not a whole evening that starts with drinks somewhere draughty. A backless or very low cut dress is a nightmare the second you step outside without a coat that actually matches the occasion, and anything heavily sequined is genuinely uncomfortable under a coat, it catches on everything. If your evening involves more sitting than standing, a works do with a three course meal rather than a standing buffet, you want something with a bit of stretch in the waist, not a rigid bodice that's only flattering while you're upright.
Before you buy, check the lining, because cheap sequins and metallics are often sewn onto something scratchy underneath that you won't feel in the shop but will absolutely feel after two hours. Check how the straps sit, whether there's any actual hold under the arms, and whether the hem moves with you or restricts your stride, since most of December involves walking fast in the cold to get somewhere warm. None of it is built for a long day. It's built for one good night, and that's really all it needs to be.