Interesting response from the supplier, considering I asked them for their recommendation on which product to use.

"Anthony,

I guess it is the first time for you to apply a clear decal on the dark coloured headstock. You need opaque white background to make decals for black surfaces items. It can not be done with normal printer but you need a white toner printer such as OKI711WT or commercial solvent white ink printer.

Regards,"

I still don't even understand if I use a white decal if it will work?

Robbo