Most people buy white trousers in the same cut as every other pair they own and then wonder why these ones feel different. Fabric that behaved perfectly in navy or black suddenly shows every seam, every pocket lining, every bit of struggle around the hips. White doesn't hide, it reports.
If you own none, start with a straight leg in a slightly heavier cotton rather than anything thin or stretchy. Thicker cloth is more forgiving on seat and front, and it holds a crease rather than clinging. Skip linen as a first pair, lovely colour but it creases the moment you sit down and shows every bit of what's underneath. In the shop, hold the trousers up to the light. If you can see your hand through the fabric clearly, you'll need to think about what goes under them, and a lot of white trousers are cut assuming you already know that. On fit, go up a size before you go down one. White has no give in the way it reads, so anything snug across the front will show a crease line at the hip that no amount of adjusting will fix. Check the waistband sits where you want it without digging, check the inside leg seam doesn't twist forward when you walk a few steps, and look at the back pockets, if they gape even slightly they'll gape more after a wash. The most wearable shades aren't always the whitest. A bone or ivory tone sits closer to skin and is kinder near the stomach and thighs, while a true bright white is more unforgiving but reads sharper against tan or dark skin. Avoid anything with a slight grey cast unless you like that washed out look on purpose, it tends to just look like a mistake under daylight.
Over time, the fabric will be the thing that decides whether these last. Cotton softens and the colour can yellow slightly at the inner thigh from friction and deodorant transfer, so a regular cool wash with a proper stain treatment before anything goes in the machine matters more than it does with any other colour you own. Line dry if you can, tumble drying speeds up yellowing. A linen blend ages differently, it goes softer and slightly looser with wear, which some people like and others find means buying a size down to start with.
They'll never be the trousers you wear without a thought in the back of your mind, and that's just the nature of the colour, not a fault in any particular pair.