Jay,
Right now, there is no way to color individual trend lines. It may be somethng thats added in the future.
Shading difference between 2 trend lines - not likely. Doing something like that with some channel indicators - maybe.
Trader333 - The specific colors are dependent on the color scheme, and also on where you are looking. For PRICE column, its exactly what you said. For bid/ask, it indicates when the bid/ask changed and in which direction. While on the raw data window, hit F1
Negative volume should not happen. Basically means that QT received a quote with a volume value that is lower than the volume on the previous quote for that symbol. If it happens often, email our support and indicate which QT version and quote source you are using.