If what you mean is changing the background color around the fields, I think there isn't any support yet, but you still can do that, through a simple hacky solution:

description
  ...
  width = min(750px, 100%); background: #cd3838 // this is where the ; will be inserted

negative
  ...
  width = ; background: #cd3838

Essentially you could insert any CSS after the width value (or just use width = ; <css> without specifying the width as well), just omit the ; at the end because the t2i framework will append that after the value.

Though, this way, upon testing on the regular AI image generator, it only works on the description and the negative prompt fields. But there's another way, using some scripts. First, define a function in the list:

setupColors() =>
  // some magic that make all of that work
  for (let el of [...document.querySelectorAll(".input-inner")]) {
    inputChild = el.querySelector(".input-wrapper *");
    inputName = inputChild.dataset.name;
    if (Object.keys(colors).includes(inputName)) {
      el.style.backgroundColor = colors[inputName];
    }
  }

And then put this at the bottom of the HTML panel:

<script>
  // Here you can define the colors of the fields that you can associate with the respective userInputs list names on the left
  let colors = {

    "artStyle": "#8b574d",
    "numImages": "#014765"
    // add more input names here if you want to

  }
</script>[setupColors(), ""]