In reply to Lukem6: As mentioned, some rope sold specifically for canyoning is designed to float.
As regards the limited range of colours, that is a deliberate policy to help avoid confusion between low stretch and dynamic ropes. White with differing coloured spiral thread patterns to indicate exact diameter is pretty much the industry normal.
In theory, colours are not limited just to white or black although the UIAA 107 standard is fairly prescriptive in some respects:
2.2. For the award of the UIAA Label, the following additional safety requirements shall be met:
2.2.1. Marking
Low stretch ropes shall be marked as follows:
(a) The sheath shall have one main colour, which shall be at least 80 % of the
visible surface (any colour is possible).
(b) Contrasting spiral threads are allowed, spiralling in one direction only,
having a maximum of two colours.
