If FT says it's authentic, it's authentic. However, glass can be authentic and not come from the original equipment manufacturer. There's no such thing as cloned glass.
Almost ALL colored tanks are colored with an external film. Exceptions would be plastic/acrylic/ultem/resin tanks. Mineral glass tanks (like cobalt blue or amber) might also be an exception, but as I've never seen one, I think they're a myth.
Best bet? Get clear, and apply your own film externally. Just use a thin water based adhesive, a removable adhesive, or cling.
Hygloss Cello Sheets - BLICK art materials
https://m.uline.com/h5/r/www.uline....rap-Rolls/Colored-Mini-Wrap-80-gauge-3-x-1000
3M Repositionable Clear Spray Adhesive, 10.2-Ounce
https://www.amazon.com/dp/B000BKQD82/ref=cm_sw_r_cp_apa_dzgIAb45GD99R
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