Found these 6-pin female-to-female cables at Seeed Studio:
Available in 100, 200, and 300 mm lengths.
By adding an extended-length 6-pin male header as shown on the right, this can be turned into a convenient extension cable for ports and plugs.
The color coding helps create a convention for ports, since their connectors are not polarized, but be careful – it looks like my batch used a different set of colors than what is currently showing on their website. And the colors also differ from an FTDI cable, alas.
Ah, conventions… so many to choose from! ;)