Found a little hack how I can get RGB vertex colors into octane
It's is using 3 UV sets, also scalar/vector ICE attributes (per node) can be transfered that way. Ideally they should be in 0..1 range.
Per vertex/polygon attributes have to be converted to per node first.
for SI 2015 SP2/Octane for Softimage 3.00 RC1 only, others I don't know