you have a custom rom, light themed?
you have to understand, if you change something inf ramework-res.apk...probably it will affect another app then. its quiet impossible to have no problems.
i think it would be easier to change the walkman background to a light color.
edit, you can also try to look into semcmusic.apk for change the textcolor, maybe you can define that inside the .xml's
also in the walkman apk you can finde out where the textcolor gets the color from. for example if its defined in the walkman apk, or in framework-res?
search a bit on xda, read a bit, and then try out yourself. you shouldnt be able to break something...
havent that much time here