Abraham H. Cannon offers description of appropriate temple garments.
Edward Leo Lyman, ed., Candid Insights of a Mormon Apostle, 1889-1895 (Salt Lake City: Signature Books, 2010): 497.
Garments worn by those who have been through the temple should be made of white materials. Union knit skirts, such as some of the sisters wear, are not proper to be worn as temple garments, but if used at all, should be over the garments.