Have you set the border width to 0 in the designer? Also Try adding -fx-focus-color:Transparent;-fx-faint-focus-color:Transparent or whatever colours you prefer to the Extra CSS field. Don't forget a semi colon in between each.
If you're going to do a lot if this fine editing, you'd probably be better adding a stylesheet.
It works here directly in the designer, are you changing any other attributes on the textarea, or using the SetColorAndBorder method on it anywhere that you've forgotten about?
Add it to the Extra CSS box in the designer with: -fx-control-inner-background:#F4F488; and it displays. How weird is that. Although it is targeting a different node I guess. So perhaps, there is your answer.
Have you set the border width to 0 in the designer? Also Try adding -fx-focus-color:Transparent;-fx-faint-focus-color:Transparent or whatever colours you prefer to the Extra CSS field. Don't forget a semi colon in between each.
If you're going to do a lot if this fine editing, you'd probably be better adding a stylesheet.