Imagine a lilac grey, like this:
https://res.cloudinary.com/wec.....ek-spring-...
Now imagine a grey with a tiny hint of brown/yellow/orange/pink in it. I have certainly been frustrated by clashing greys myself. When you look at each item on its own, it reads grey, but when you put them together the clash between warm and cool toned greys can really be a problem. I own multiple grey items that definitely clash horribly. I've found it easier to make warm-cool grey combinations work if one of the greys is dark and the other light.
The same clashing issue is true with blacks and whites. You think you have a completely clash-free wardrobe, because everything in it is black... but when you try putting two items together, you discover that one is warmer-toned than the other, and it looks terrible. Sometimes you can get away with putting a contrasting layer of something else between them, but often not. With whites too, whilst mixing whites and creams can work, if the whites are too similar, one white can end up looking a bit yellow compared to the more blue-white sparkling new item you are trying to wear it with.
I hope this helps.
Sarah
