Hello,
You can already change the border and font color for video files with external subtitle files in PowerDVD's subtitles settings. Please have a look.
As for your suggestion, this is a user forum and CL does not monitor so please submit your software suggestions directly to CyberLink:
https://membership.cyberlink.com/support/customer-services.do
Cheers
PowerDVD Moderator
Please direct any sales or technical issues to CyberLink's customer support team:
Sales or installation related issues:
https://membership.cyberlink.com/support/customer-services.do
Software technical issues:
https://membership.cyberlink.com/sup