Start with the dress
The dress is what shows up most in photos and videos, so choose it first and build the palette around it. Use its color as the main one, then add a metallic (gold, silver or rose gold) and a neutral for the linens.
Watch out for the venue lighting
Quinceañeras are usually evening parties with colored lights. Very pale shades can wash out under that lighting, while deep ones like royal blue, emerald or burgundy hold up. If you can, visit the venue at night before you decide.
Coordinate the court and the family
Decide early what colors the damas, chambelanes and parents will wear, so everything looks put together during the waltz and in photos. A shade darker or lighter than the birthday girl's helps her stand out.