Just to clarify what tightlining is (or at least what I was led to believe it is!)
It's not the same as lining your inner rims.
It is using a flat brush and 'pushing' the brush into the base of the lashes where they meet with that skin. On upper lashes, it's done under the lash line, so that it doesn't look like eyeliner. The results are meant to be subtle. The goal is to define your eyes without making the eyeliner obvious. If applied well, it will make it appear as if you lashes are full because at the base of your lashes, the whole area will be dark but without that obvious line.
If you want a more noticable line, then you would do the same procedure above your lash line, and then as you remove the brush, you would sweep it upwards as much as you wish.
In my experience cake (aka a very dry, hard almost like eyeshadow) eyeliner is best for getting that fine, perfect line. As an added bonus, the Laura Mercier one is waterproof.
As for whether it's best for dark or light ladies, I'm a super pale redhead and I use the black cake liner daily and it looks very natural. So I think this method should suit most of us.
hope this helps!!