Background color of Fill in the blank text box

Hi

I am adding Fill in the Blanks question in the software demo-based interactive video activity. The software is predominantly of White background. Now, when I use the Poster option of FIB question, the FIB background looks almost same as the software screen behind it and the activity is not so prominently visible (despite the pop-up kind of effect with shadow).

So, is there a way to change the FIB question background? 

Sreekanth