You can spot a good pair of tailored trousers from right across a room, and it's not about the fabric catching the light. It's the way they sit at the waist and fall straight from the hip, no pulling, no pooling at the ankle. A poor pair does the opposite: they bunch at the crotch when you sit down, they ride up when you walk, and by four in the afternoon you're tugging at the waistband under the desk like it's done something to you personally.
For colours that you'll actually reach for, I'd go for charcoal, navy or a soft stone before true black, because black in a cheap fabric can look flat and a bit school uniform under office lighting, while a charcoal or navy with a bit of depth to it looks considered without trying. A mid grey is the one I wear most, oddly, because it goes with almost everything I own and doesn't show chalk dust or coffee drips the way black does. Before you buy, check the waistband construction, whether it's a proper curved waistband or just a flat strip of fabric folded over, because the flat ones are the ones that gape at the back. Check the lining goes all the way to the knee, not just a token few inches, and sit down in the changing room, properly sit, because that's when a bad crotch seam makes itself known. Check too whether the fabric has any stretch in it, because a small amount makes a real difference by hour eight and doesn't show at all. What they clash with is anything equally structured on top, a stiff blazer with a stiff trouser just looks like a costume, so I'll put mine with a soft knit, an oversized shirt left slightly untucked, or a simple t-shirt, and leave the sharpness to do its job on its own. They don't sit well with heavy boots either, in my experience the proportion goes wrong and the leg looks shortened, so a loafer, a low heel or a clean trainer works better.
Where they're the wrong choice is if you want something to move in properly, for a long day on your feet or anything where you'll be crouching, lifting, chasing a child across a park. The tailoring that makes them look sharp standing still is the same tailoring that fights you the second you need to really move, and no amount of stretch fully solves that. For sitting at a desk, meeting a friend for lunch, or travelling somewhere you need to look like you made an effort without actually trying hard, they're exactly right.