What contrast checker do you mean? And what do you mean by “colours they suggest”? I don’t think WCAG suggest any specific colours unless you are aiming to be accessible for colour blind audience, only contrast levels.
What I meant by “Colours they suggest” as a test I entered my two colour I want to use for a new brand. One of the colour failed so I tested it on the slider to see which colour tone would get approved.
It’s hard to comment honestly. I mean if two colours you wanted to have for a brand are for use on the logo or some graphics then you could use whatever you want. But obviously not all colours look good when you use one as a background and another as text. And that’s what this tool checks
Sure. But its just a rule of thumb. Following these directions ensures proper readability for users with not perfect sight. Also increasing text sizes helps of course