Yes it is possible to change the color of the progress bar.
What you need to do is copy the skins folder to somewhere like your documents folder; then in explorer you need to rename the folder you have just put into your documents folder.
Next in explorer open that renamed folder locate the main.xml and open it in a proper like editor like notepad++ and change the name of the skin and save the modified main.xml.
Then locate the image named PlayerBar_SliderPosFront.png in that folder, open it in an image editor and change the color to a more acceptable one and save it.
Finally copy that folder back to the MC Skins/Standard View folder.
NOTE if you don't change the Skins Folder Name and the Skin Name in the main.xml file MC will replace your modified skin with the standard one if and when you install an MC Update.
