Looking at a photo, the color of the bulb should just be white. If you place a amber bulb under the red lens, it wont show up very well. As for the screws, they are most likely the rotating housing type. Grab the bulb housing and rotate counterclockwise till the bulb is loose, then just pull back and they should pop out.
you should be able to access them from your trunk.. behind the carpet.. as far as color the amber will work just fine and i believe when you access the old you will see the same color bulb! as far as tools your hand should be enough to pry back the carpet and twist out the socket!
To access your tail light bulbs, you will need to open your trunk... Once you open the trunk you will see a number of plastic wing nuts on both sides of the trunk opening. To take the housing off, you need to unscrew the wing nuts and pull the tail light assembly off. Then you can change the bulbs. To replace, just line the assembly's bolts back up with the holes and put the wing nuts back on. I believe you will want to use clear bulbs for the tail lights, since the housing is all red.