IMO the eBay sellers film is probably just 1.5mil PGS or GS polyester lamination film. PGS films are treated to receive ink and printing. Not all lamination films are PGS, the labels will be marked as such.
PGS = Printable, Gluable, Stampable.
GS = Glueable, Stampable.
Yes, you can paint the adhesive side with transparent floral dye very easily and it will adhere just fine. I did a plane like this last year. As an experiment, I used the floral dye on the balsa as well. Very lightweight. The film I used is .75 mil and it is very light but also very tough. I have a few thousand feet of the stuff...it should last several lifetimes!
This is my Trailblazer airplane before I installed the foam Gotcha wing. It looked great.