Do cargo trousers actually suit anyone who isn't twenty two and built like a reed, or is that just how they photograph on other people? They do, honestly, but the fit has to be right through the hip and thigh, with room in the leg rather than everywhere, otherwise the pockets just add bulk exactly where you don't want it.
I wear mine with something fairly plain on top, because the trousers are already doing a lot of visual work with all those pockets and seams. A fitted t-shirt, a simple jumper, a shirt tucked in at the front and left loose at the back, that sort of thing. Trainers are the obvious pairing and they work, but I've had just as much luck with a loafer or a low boot when I wanted to look like I'd made an effort without actually trying very hard.
They're best in the in-between weather, autumn mornings, early spring, that stretch where you need something sturdier than summer cotton but a proper winter trouser feels like overkill. I reach for mine for a weekend that involves walking somewhere and then standing around a market or a gallery for a few hours, nothing fast, nothing that needs stretch, just something that won't crease if I sit on a step for twenty minutes. They're less convincing for anything smart. I tried a pair at a dinner once thinking the fabric looked dressy enough in the shop lighting, and spent the evening aware that everyone else was in proper trousers and I was in, essentially, a very nice boilersuit bottom half.
Colour wise, I'd steer away from true black unless you want them to read as a uniform. Olive, a soft stone, a faded khaki, those wear in nicely and go with nearly everything else you already own. Anything too washed out shows marks fast, which matters because cargo trousers end up doing outdoor duty whether you planned that or not.
The fabric is the whole story with these. A decent cotton twill softens after a few washes without going thin, and the stitching around the pockets is the bit to watch, cheap ones start pulling at the corners within a few months of actual use, not just wear. Mine have been through a washing machine more times than I can count, shoved in a bag at the bottom of a wardrobe for a season, dragged out again, and the only real change is that the colour's gone a shade paler and the knees have that soft, lived in look that no amount of ironing puts back. They stop looking new fairly quickly, and then they just look like yours.