This can be done via adding the following CSS code:
[class^="FormLayout__Error"],[class^="FormFieldLayout__Error"] {
color: rgb(143,0,255);
}
[class^='FormFieldLayout__Container-sc-']:has([class^='FormFieldLayout__Error-sc-']) [class^='TextControlBase__TextControlBaseContainer'] {
border-color: rgb(143,0,255)!important;
}
However, itโd be great to have this right in the widget settings, too!