I feel your pain. I have often taken an item back to my consultant (just happened to be wearing it when i saw her) and asked for her opinion. I noticed that anything that was 'right' she would make a fuss of, anything not great for me, she would say lovely and move on quickly to something else. Sigh...
You have already noticed that it is much easier to evaluate one colour compared to another, rather than by itself, in isolation from other colours: you mentioned a navy that cannot be distinguished from black.
The difference between warm and cool colours seems important, but difficult to distinguish for me. The shop lighting can make a big different, so seeing the colours in daylight is always going to be helpful. I also keep a square of gold and of silver lame, because most colours look better with one or the other, a clue to warm v cool basis for the colour.
The gold/silver thing was one of the first things that got me hooked on colour analysis, i saw a talk, where as part of what I at first took to be the general decorations, the consultant had four pieces of material, two had a silver necklace resting on them, the other two a gold necklace. At the relevant moment, she swapped the two chains over. On the 'wrong' colours, what had looked like expensive necklaces suddenly looked like the sort of chain you might expect to see on a sink plug.
I was convinced that it is worth seeking out colours that look good together