How to change background color of subtitles?


I have a philips PET810 portal dvd player.
When I play dvd’s with divx and subtitles on, alle goes fine.
But the subtitles have a blue background.
This is very annoying and would like to remove the background color of my subtitles.
Also if possible increase the size of the subtitles a little, but this is less important.

Someone know how this can be done?