No white thread on white cotton, that really doesn't inspire me - so surely I should be working with materials that do? Hence the 'less traditional' fabrics I'm embracing (although cotton-a-broder is still my favourite thread of choice.) As for the name 'whitework', it refers more to the traditional techniques encompassed by that name rather than a specified colour scheme.
And then I got hold of some black latex.... and proved it is actually possible to stitch on, much to my surprise. The key is patience, to go very gently, and remember that one little rip whilst working it will destroy the entire sample. I'm still not sure as to its stretchability post-embroidering: the sample can stretch a bit, assuming you'd need sufficient 'give' to get a garment on, but I doubt there'd be a great deal of stretch without distorting the stitching.
Nobody else really seems to be embroidering into latex, at least as far as I've seen: probably for good reason, but it's an area I want to consider playing with. How to embellish it, and what to do with it afterwards.