To jitter color with user data, you need to connect an aiUserDataInt to the data input parameter, like this:

The user data is an mtoa_constant attribute on the shape.  For example, if add an extra attribute named mtoa_constant_jitterID to some shapes, then you can use aiUserDataInt to read the jitterID.

jitterID is set on the shape

Jitter by user data (with a little jitter per face too)

aiUserDataInt reads the jitterID

If you want to use the shapes as standins, and be able to set the jitterID in the scene, then export the shapes without the mtoa_constant_jitterID attribute. In the scene, you’ll be able to add mtoa_constant_jitterID to the aiStandin node. The aiUserDataInt node in the ASS file will use that jitterID.