I would say light colours do not need a fancy finish to look good (i.e. gloss white looks as good as pearl white), whereas dark colours need more fancy to look good (i.e. pearl black looks better than gloss black).
However the price Volkswagen demand for Onyx White is not worth it, when you consider it does not cost much more to paint a car in pearl effect compared to metallic or non metallic (a friend of mine who is a sprayer said it only costs a couple of pounds more to paint do a metallic or pearl effect compared to gloss and said only black demands a higher premium but not by much)
I was told by the dealer you would be nuts to order Onyx White as its very hard to respray if you ever have any body work damage. Im not sure how true that is...
From what I know it is harder, because it is impossible to replicate the finish regardless, unless you can get hold of the exact same spray gun (because every individual spray gun sprays the paint slightly different)
The easiest paint to fix in is non-metallic, because you can blend it in or use polish to compensate (and eye ball it), whereas with pearl finish their is another factor to determine a good fix (how it reacts to sunlight makes it harder for the painter to fix) and professional repairs do not use the exact same paint, because the colour does naturally lose its colour over time (red is the worse for this one from what I have been told).
The worst to fix is matte paint however, because you cannot blend and you cannot use polish to compensate (a friend of mine had to work on a matt grey BMW M3 with stone chips and took 4 attempts to make it presentable).
The easiest colour to fix is pretty much a gloss white from what I know.
(please note I am no expert i worked as a spray shop assistant i.e. sander for 3 months when I was younger and chatted alot with the sprayers whilst waiting for the paint to dry)