The gray machines
Electrolux started selling kits for after filters during the gray color scheme. As far as I know, and I'm pretty sure of it, Electrolux never offered a kit to match the first Epic upright in dark blue. The starter kits came with the frame, which used really strong adhesive with a peel-off cover to attach to the body of the upright around the suction motor exhaust. You had one chance to get that on correctly. Once that was attached, it adhered strongly enough that the actual filters could be snapped out for changing without tearing off the mount.
These were introduced partway through the gray production years, and I'm pretty sure they became standard equipment on new machines after their introduction. I don't recall seeing an oyster/fog or newer machine without an after filter, but I might be wrong about that. I'm pretty sure Electrolux never stopped including the spongy pre-motor filter that sat underneath the bag over the intake.
Just like all of the again Electrolux machines, every color scheme of which I have liked, the replacements in the proper colors aren't available, so now the machines look ridiculous if you don't have a supply of the original filters, the worst example of which is the Guardian, which looks terrible with a completely different, and huge, HEPA filter atop it.
Hope that helps. I was at the peak of my Electrolux enthusiasm in the 90s when these things came out.
