What does "Dark Background " mean TT terminology

I would add to Johnnatais's comments that a blacker background with a TT or CDP usually implies more color and constrast in the music itself. Critics sometimes use the opposite term "whitishness", to describe a lack of constrast or color. Of course all these terms are analogies...

The subtleties of the leading edge of notes, note decay, reverberant space, hall depth, etc., that contribute to a realistic rendering of music, seem to be revealed in contrast to dead silence (blackness). But it's debatable whether the absence of this desireable attribute is caused by a higher noise floor, or by false signatures imposed by lesser equipment at the threshold of audibility. For example, when the music isn't playing, a good SS system is generally quieter than even a great tube system due to tube noise. But to me at least, the tube system can be just as effective at communicating the subtleties of music on the verge of silence. In any case, the presence of modest tube noise in the background does not make it any less "black" sounding.