What Does "White On Rice" Mean?

"I've heard the expression 'like white on rice,' but I'm not really sure if I'm correct in understanding what it means.  Can you find me the information?"  English has some very unusual phrases that the patrons and staff of the Newton Falls Public Library have found to be interesting.

Our search began in the library's reference collection.  On the cover of Cassell's Dictionary of Slang by Jonathon Green, which is, according to Evening Star Standard  reviewer Jonathan Meades says ". . . a terrific piece of work - learned, entertaining, funny , stimulating." It has 1312 pages of definitions, from  "a n. 1[20C](W.I./Guyn.) a general term for dislike. 2 [1940+] (US) used as euphemism for ARSE" to zweideener n. [late 19C] (Aus./N.Z.) a two-shilling (10p) piece." Our library staff was intrigued it. Some of the words have a great variety of meanings. For example, dog has 34 entries, and 56 definitions.  It was interesting to browse through the book and see that it includes slang from as far back as the 16th century up to modern day.  "Like white on rice," the expression, for which we were searching, came into common usage in 1980 and continues to be used today.  The origins of  the phrase is attributed to US Black.  It is defined as "very closely [rice is white itself]".