Everything I've seen and heard is that the green caps and writing indicates an "eco" friendlier lamp; lower mercury content, not non-mercury content.
According to the websites posted here, TCLP (toxicity characteristic leaching procedure) compliant lamps "...may not prevent (mercury) leaching over long periods under real landfill conditions." Also: "Although it is legal in many states to dispose of TCLP compliant lamps as nonhazardous waste, this practice sends mercury to landfills or, worse, to municipal waste incinerators, and thus contributes to mercury pollution."
We here at the Department of the Navy handle even these lower mercury content lamps as "universal waste" and recycle them. I end up doing quite a lot of lighting here and turn in boxes by the hundreds; and that's just my shop among several.
And finally the conclusion which I totally agree with given the shear volume of these things we handle:
"Conclusion
The TCLP status of fluorescent lamps is not necessarily
the best indicator of their potential environmental
and health impacts. Consumers who wish to reduce the
impact of their lamps on the environment will (1) select
lamps that contain the lowest mercury content available
for their particular use, and (2) recycle all lamps at
end of life, regardless of their TCLP status. "