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That muddy green color is probably the tinted/frosted faceplate/safety glass, bonded to the face of the tube. FJ's have a bonded faceplate, that sometimes develops mold or gunk underneath it, leading to what has become known as picture tube "cataracts". The 21FBP22, however, has no bonded faceplate, and was intended to be installed in sets that have safety glass in front of the tube already.
Now, if you got your first FJP from a picture tube rebuilder, then it might be missing it's bonded faceplate. On most non-Zenith tubes, the faceplates come off when it's heated enough, which is a part of the rebuilding process. The faceplate isn't really needed, so probably gets left off a lot (AFAIK). Cataracts on these tubes is cured by carefully heating the faceplate with a heat gun to soften the glue, getting it off, cleaning off the glue, and taping the faceplate back on with packing tape along the edges.
Zenith tubes, OTOH, have a bonded safety glass that's affixed to the tube with something that doesn't really respond to heat. They tend to get a "green halo" when the bonding agent deteriorates. I think the procedure for removing the faceplate from one of those involves nichrome wire and a car battery.
-Ian
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