Info is taken from Wikipedia:

This is a classical style singer pack with a solo female vocalist. In contrast to the "Realivox Ladies" product, Blue is a more complex package with advanced features. Her vocal is complex with 12,000 samples with 32 samples per sound covering two and a half octaves of singing vocal result, while closing consonants have 192 samples for certain sounds such as "t". All six vowels contain legato results, this is also included for humming sounds sound as "mm". She also contains polyphonic legato capabilities. She is designed to be a go-between vocal and has realistic tones. The samples are combined to build words, with the transition between the sounds being almost invisible.

Examples of her voice: