I'm not sure if Edyta Sitar does them by hand - I know she endorses Aurifil thread boxes that have 'Laundry Basket' on them. I did her Reaching Out, seen
here, with Madeira and Superior embroidery thread because that's the effect I like - a slight sheen for definition. Mine is done with toning colours, including variegated.
I wouldn't use invisible as I believe that after a time it does perish. I'm a recent silk convert. I've only used it to hand stitch the back of a binding, but loved the way it didn't twist and just sank into the fabric
. It would be pricey, but you'd probably only need a few neutral colours.
Use the thread
you like the best and don't worry too much about anything else.
Happy quilting.