I collected wild Finger Lime seed from Nth NSW, one orange fruited one green fruited. I grew those seeds and the fruiting plants were identical to the parent, except slight differences in fruit size ( but not skin and pulp colour ).
As far as see it, seed would be true to type, except for the fact that Finger Lime seed sellers often grow the plants in multi variety collections or plantations, so cross pollination is more likely than with the isolated wild plants I found.
Also some of the prized varieties have more complex skin pulp pigment colour combinations, so pigment variable offspring could be more likely.
( plus X pollination on top of that too ).
If a particular Finger Lime plant produces pigmented fruit, attractive to birds or animals to spread the seed, it doesn't make much sense for the plant to produce wildly different coloured fruit that may be less attractive than the parent.
I think if you could get isolated non X pollinated seed of Finger Lime varieties, it is more likely they will be true to the parent. There are still other factors to think about like fruit setting ability etc. The whole package is probably only available by grafting.
As far as I know all existing C.australasica Finger Lime varieties are wild collected and none have bred by deliberate cross pollinating.