Some of my wedding pictures have color that it is so vivid that my breathing changes when I look at them. The primary photographer who color balanced them is known to be a “naturalist,” so the images are not just boosted in Lightroom. The flesh tones are natural. I'm even a little pale, though those with tans look like they have tans.
Both photographers were shooting with several L-series zooms.
… and thus you're believing that the colors are due to the lens?
By far, the most important factor in getting the colors right is the
light at the scene. If you mix ambient light with flash, the flash should have the same temperature as the ambient light, for instance. Otherwise no lens or photoshop trick in the world is going to help you. Getting the light right is the first step.
Second factor: the photo needs to be properly exposed. Properly here means that it is exposed the way you want it to.
There are many other factors beyond the lens:
(1) The RAW conversion: no matter if this is done in-camera or with a tool of choice, this will have a significant impact as well.
(2) Image manipulation via Aperture/Lightroom/Photoshop/Pixelmator/whatever.
(3) ISO: the lower the ISO, the larger the dynamics (roughly speaking). If you shoot at higher ISO, your images will be flatter.
As you can see, there are quite a few other factors beyond the lens. It is true that the lens enters the game as every lens has a unique color characteristic (some colors are absorbed more strongly than others). Also if the lens has more contrast, the photo may have more pop.
I would definitely warn you against concluding that L = more vivid/more natural/whatever, you will most likely be disappointed.
Second of all, the terms `natural' and `vivid' are on opposing ends of the spectrum: more vivid colors means
increased saturation of colors. Hence `less natural.'
1. I see that the EF 85mm f/1.8 USM prime delivers the sharpness of the 24-105L, but will it give that knock-you-out, Vivid color?
See above.
2. My other question is, how is this “vividness” measured? The EF 28-105mm f/3.5-4.5 II USM
(here) I’ve used was tested to have only “relatively minor” chromatic aberrations in
this review; but CA’s or not, this lens’ color is pretty dull.
It's just not a very good lens. According to the review by photozone, the lens performs poorly in low-contrast situations. More likely than not, you'll benefit from upgrading to a more suitable lens, e. g. Tamron's 17-50 mm f/2.8 or Canon's 17-55 mm f/2.8. Both have very good optics and if it weren't for Canon's marketing, optically, it could be an L-grade lens (Canon's L lenses `have to be' full frame lenses).
I was originally asking about the EF 50mm f/1.4 USM to use primarily as another low light prime, but I realized I simply cannot control a DOF of 3-4 inches that I would get from f/1.4 (3 ft. field of view), and probably not even f/2 (6 inches) with a moving subject. And, at high ISO, I can’t just shoot wide and crop in post (to gain DOF) because this effectively increases the noise at image level.
Then practice. If you are into portraits, being able to separate your subject from the background is an
absolutely essential skill that takes practice to master. 50 mm on crop sensors is a nice focal length for portraits.
85 mm is already a very different story, it condenses everything much more and I have a hard time to do indoor portraits with that focal length (I don't do studio stuff).