The Collaborative International Dictionary of English v.0.48:

'Ecru \['E]`cru"\, a. [F., fr. L. crudus raw.]
   Having the color or appearance of unbleached stuff, as silk,
   linen, or the like.
   [1913 Webster]

WordNet (r) 3.0 (2006):

ecru
    n 1: a very light brown [syn: beige, ecru]