Ecru describes the shade greyish-pale yellow or a light greyish-yellowish brown. It is often used to describe such fabrics as silk and linen in their unbleached state. Ecru comes from the French word écru, which means literally 'raw' or 'unbleached'.
In the 1930s and before, ecru was considered to be the same colour as beige (a synonym or alias for beige), but now ecru and beige are regarded as two different colours.
Source of color: ISCC-NBS Dictionary of Color Names (1955)--Color Sample of Ecru (color sample #90):