In Hidden Meanings in Chinese Art, p.135, T. T. Bartholomew remarks, that because of its green (qing) and white (bai) colors, "the Chinese cabbage (Brassica rapa var. glabra) is a pun for qing and qingbai, both meaning 'without stain,' as in a clean personal record." Bartholomew also notes that the second character of "cabbage" (cai) is a pun for "wealth," and that the Chinese believe that eating this vegetable will help one gain prosperity.
Compare with a semi-transparent green glass baicai-form snuff bottle illustrated in Moss, Graham, Tsang, A Treasury of Chinese Snuff Bottles. The Mary and George Bloch Collection, Vol. 5, Glass, pp.376-377, pl.846.