You can still be grounded through paint, and as Jack said their are always some areas that are not painted over if you're concern is that high.
Honestly (and just wondering here) how many of you have built a computer and got a static shock while doing it? How many of you have had a static shock inside your house in the last several months? I almost never get shocks (apart from my mums car which is a nightmare lol) and have yet to EVER get a shock building computers.
I really like the corsair 600t but worried about working on it without touching a metal part of it since the whole thing is painted black as well as my psu.
Is there any way around this or am I worrying about nothing?
There is no need for concern. If anything, paint may reduce a metal's ability to transfer heat/electricity. When working on the interior of the machine, you should ground yourself by a wrist strap (which most of us fore go) or by touching the chassis; preferably an un-painted surface to discharge any static current you may be carrying.
And its true, a current that is too small too detect or feel is plenty to destroy components.