It would be great to be able to choose the color of the subtitles. I would suggest these colors: white, yellow, light green, pink and sky blue. Sometimes it is better to see the subtitles in a different colour.
I would also like to suggest to allow to change the font size of the subtitles. I would like to be able to choose sometimes a larger font size.
I like to watch TV programs while I am cooking. While cooking, I am sometimes located far from the screen so it is hard to read well the subtitles. In these occasions it would be very convenient to be able to change their color and font size.
I’d really love the option of a bigger font since I tend to watch kdrama while cooking as well
And the color option for subbers has some merit as well. However, the viewer should still have the option to watch everything in regular white if they prefer so. For example I feel that text in different colours disrupts my personal viewing experience. (I’ve seen some anime fansubs, where different characters had different colored subtitles.) Also, colourblind people might have problems in distinguishing coloured text front the background…
This doesn’t mean that I oppose the idea. I wouldn’t use the colours, but some other people might want to.