Start with the room, not the mood board
The venue has a palette whether you chose it or not. Carpet, walls, curtains, chairs, timber, metal finishes and the colour temperature of the lighting are all in every photograph you will take, and none of them are moving.
A palette developed without them is a guess. Go and stand in your venue, ideally at the same time of day and year as your wedding, and look at what is already there. A cool grey scheme in a warm room with gold fittings and cream walls will fight the room for the entire night.
This is why the same palette produces completely different results at a finished room with strong metallic detailing and a large neutral ballroom. One has a palette already. The other is waiting for yours.
Lighting changes everything
Colour is a property of light, not of objects, and wedding lighting is rarely neutral. Warm venue downlights push everything amber. Coloured uplighting, common in rooms with built in LED, will wash your linen and florals in whatever colour is selected.
The practical rules are simple. Decide the palette and the lighting together rather than separately. Look at samples under the actual lighting rather than at home. And remember that most of your reception happens after dark, so the daylight version of your palette is the version you will see least.
Pale and cool colours suffer most under warm light. Whites go cream, greys go beige, and soft blues can disappear entirely.
A structure that works
Rather than picking colours you like and hoping, use a proportion. Roughly seventy percent a dominant neutral, twenty percent a secondary colour, ten percent an accent.
The dominant neutral does the heavy lifting: linen, drapery, the large surfaces. The secondary carries through florals and detail. The accent appears rarely and deliberately, in the places the eye already goes.
This is why restrained palettes read as expensive. Three colours in disciplined proportion looks intentional. Six colours in equal measure looks like nobody decided.
Season and flowers
Flowers are the least controllable part of any palette. Colour varies between crops, and a variety photographed in one arrangement will not be identical in yours.
Choosing in season is both cheaper and more reliable, since in season varieties are better conditioned and hold their colour longer through a long reception. Build the palette around what will genuinely be available in your month rather than around a photograph taken in a different hemisphere. More on how florals are coordinated.
Where colour carries meaning
In some traditions colour is not a preference. Red carries luck and celebration at Chinese weddings, and white has traditionally been associated with mourning, which is worth discussing with older family members before committing to an all white reception rather than discovering the objection on the day.
At Indian weddings, different events in the run carry their own conventions, and the haldi in particular is usually built around yellow and marigold. Green carries significance at Afghan henna nights.
None of this means you cannot choose what you want. It means the conversation is worth having early, and there is usually a resolution that satisfies everyone, such as holding the traditional palette for the ceremony and taking a freer hand at the reception.
Test properly
Get physical samples of your linen, your napery and your florals, put them together on a table, and photograph them on a phone under warm light. The phone matters, because that is how most of your guests will record the night.
If it holds up there, it will hold up on the day.