Change the opacity of Background for captions

[#1]

Hi, i would like to find out how i can change the opacity of the background of captions. I understand some one here points out there i can change using the inkdropper icon, but I do not have this icon in my options. Please help. Thank you very much. 

[#2]

Hi, i would like to find out how i can change the opacity of the background of captions. I understand some one here points out there i can change using the inkdropper icon, but I do not have this icon in my options. Please help. Thank you very much. 

[#3]

 

[#4]

You can only change the background on open captions.

Close captions are set.

[#5]

Thanks guys! 🙂