From a 3M document: DISCONTINUED BY 3M 02/27/06 REPLACEMENT PRODUCT IS 398FR*** A 7.3 mil. flame retardant, glass cloth for sealing seams on aircraft ducting and cargo area panels. Tape meets flame retardancy of military spec. A-3316B, F.A.R. Part 25.853(a) and F.A.R. Part 25.855(d).
The tape is white, although in the picture it appears blue from the side due, I assume, due to the adhesive. It is available to buy online – just search on the above part number.