altColor in UCSC track setting

Many track types allow setting a color range that varies from color to altColor. For instance the CpG Island tracks use the altColor setting to display the weaker islands, while the stronger ones are rendered in color. If altColor is not specified, the system will use a color halfway between that specified in the color tag and white instead.

Be aware that wiggles with negative values are drawn in altColor not color as positive values are.

Hierarchical structure of UCSC Genome Browser track hub

UCSC Genome Browser tracks can be organized into groups by using the container multiWig, compositeTrack on, and superTrack on lines. Supertracks can contain composite tracks and container multiWigs, but not vice versa. With supertracks, composite tracks, and container multiWigs, children will inherit the settings from their parents, but can override their parent settings within their own stanzas.

Here is their hierarchical relationship:

superTrack on

|==== child tracks (bam, bigBed, bigWig or vcfTabix)

|==== container multiWig

     |---- child track (bigWig)

|==== compositeTrack on

     |==== view

         |---- child track with subGroups setting (bam, bigBed, bigWig or vcfTabix, but not mix)

         |---- child track with subGroups setting (bam, bigBed, bigWig or vcfTabix, but not mix) 

superTrack also allow to mix other supported types of hub tracks: bam, bigBed, bigWig or vcfTabix.