#18 NWOT  HALSTON Woman‘s Champagne Long Nightgown  Size: 1X
Pit to pit-21 in
Bust-42/44 in
Length-54 in

This color can be described as ivory or cream.
Depending on the lighting and the specific brand, this shade is also often called:
Champagne - if there is a slight golden tint.
Sand beige - if the tone is more muted and natural.
Alabaster or ecru - for lighter, milky variations.