I hate to pull the "you must work on trivial projects" card, but really, this article points out one very solid reason to use a CSS pre-processor. If you've never felt the pain of managing the colors, with gradients and everything else, I'm not convinced you've worked on a decent-sized project--that or you love project search/replace.
Try out the SCSS syntax (or LESS), might warm you up to it a bit more.
Trivial projets? Perhaps. How many layouts does one need before a project becomes decent-sized? In the several years I've been doing web development professionally, I've changed the colors on a site exactly zero times - it just never comes up. I have wished for variables in CSS from time to time to make things more readable, but really not enough to care about SASS.
In the end I find that if I organize my CSS well, changing things like colors really isn't such a big deal. Like you say. Find/Replace.
Oh well. Either it will pass as a fad or I will one day be forced into the light.
Perhaps it's the type of design projects that are undertaken and the work style of the designer.
In the situations where a designer provided .psds for me to transform into html/css, no I haven't had to modify anything. But then, the iteration on the design happens with the other guy, and he does it in photoshop. If a change happens, he just sends me the new asset images, and I just replace them in the repo.
The times where I'm the one doing the design work, I end up switching things up a lot. This is because I don't do my design work in photoshop, but rather in the browser with actual html/css. So even while I'm iterating on something by myself (before having even shown the client anything), I'll switch colors up constantly trying to get something I'm okay with.
It's not just something like changing colours, though i have had to do that - it's applying the colours in the first place.
Rather than trying to remember a previous hex, or looking it up, you can think ok, this should be the darker highlight colour - and as you say, looking later you know which colour that is.
It's not just colours - a good example is a clearfix. Rather than add it to the markup, you can add it via css, and of course if you change it, you change it once.
Try out the SCSS syntax (or LESS), might warm you up to it a bit more.