A black-and-white long-sleeve view shows a quiet pale dress shape here. The front neckline runs straighter, with slightly raised shoulder areas. A defined waist divides the bodice from a broad skirt surface continuing down and behind. Hands rest before the middle. Grey tones reveal lines and differences in lightness without explaining the exact actual colour of the garment, keeping shape information separate from a colour comparison still to be made.
Use this picture as a silhouette reference first. Do you want long sleeves beside a broader lower area, or a quieter shoulder shape? Indicate those lines at a fitting and add real colour samples for your tonal combination. Wanting similar lightness is different from having already confirmed a match with veil or gloves.
Ask to see the actual candidate with relaxed arms and inspect side and back too. Try walking and sitting with your shoes. Add the intended pale companions afterwards and compare their relationship in the same light. This uses the visible silhouette precisely without assigning colour information to a black-and-white photograph that cannot supply it for your full outfit.