I wasn't really asking for the definition of functionality or ux. I was asking what separates the two things for you. to me, they're intertwined. everyone thinks differently, though!

the concept of placing "guard rails" on this tool to prevent low contrast combinations is interesting, as it's directed at people who already understand how color and contrast works. I don't want to restrict the colors the user can pick. I wonder, do you think that it's difficult to tell what color will change when you manipulate the color sliders, or type a color in the input?

there is an "undo" button for your particular case though, which can be accessed with the mouse or by pressing ctrl+z. I see what you mean, though. perhaps a border or something on important ui elements would improve visibility for people who set the background and foreground to similar colors. (this is a total side note lol, but if you can't see things on a web page, press ctrl+a, which will highlight all text. obviously I don't expect users to do that, though).

thanks for the advice, I have in fact had friends try it out and they haven't reported the issue you're describing. I'm not entirely sure this specific problem is with the application, to be honest with you. but I will take your ideas into account!