HTML

<script src="https://cdn.jsdelivr.net/npm/a-color-picker@1.2.1/dist/acolorpicker.min.js"></script>
<textarea id="editor"></textarea>
        

JavaScript

const editor = new Jodit('#area_editor', {
  buttons: 'brush'
});

// After open will add custom buttn in default color-picker
editor.e.on('afterGenerateColorPicker', (form, extra) => {
  // Make button
  const elm = editor.create.fromHTML('<button class="jodit-ui-button">Custom</button>');
  Jodit.ns.Dom.detach(extra);


  extra.appendChild(elm);


  //
  let selectedColor = null;
  //
  elm.addEventListener('click', () => {
    // On Click - show dialog witch color-pciker
    const dialog = Jodit.Alert('', 'Select custom color', () => {
      // On Ok apply this color
      if (!selectedColor) {
        return;
      }
      //
      const style = new Jodit.ns.Style({
        style: {
          color: Jodit.ns.Helpers.colorToHex(selectedColor)
        }
      });
      //
      style.apply(editor);
    });
    // Init custom color picker for dialog's content element
    AColorPicker
      .from(dialog.dialogbox_content.firstChild)
      .on('change', (picker, color) => {
        selectedColor = color;
      });
  });
});