On the wire harness for the new Saleae products (released September 2014) all ground wires use black wire with black heat shrink. Channel 0 and channel 8 signal inputs also use black wire, but with white heat shrink with the channel number printed on two sides of the heat shrink.
The wire colors were originally selected to match existing products on the market, which also match the numbers 0-7 on the resistor color code chart, and the wire numbers 0-7 in MIL-STD-681.
If you would like to suggest an alternative, please do so here, on our ideas & feature request tracking system, ideas.saleae.com:
trello ID: 56398122199cb2630784470c