Alex, I only ever used grapefruit, and always the ruby red, because it's the only one I find palletable!
Who knows why HC does things the way she does ... as far as saying "use grapefruit"? Cause she's like that.
The key is CITRUS. Citrus causes strong muscular contration in the liver and gallbladder. There are positive flushes reported with any # of other citrus fruits.