Yup, its white or pearl white for the sturmtiger interior.
If you only have brushes you could still do the camo.
First paint the kit completely dark yellow (XF-60 if you use Tamiya) afterwhich paint the camo colors by using masks.
Here is an article in FSM that would help you in brush painting
Basics of Brush Painting Cheap masking suggestion:
First cut the shape of the camo you want using masking tape. Place the tape on the area where you want the camo to be. Paint over the area using your brush. Repeat process until you completed the camo... you will end up with have hard edged camouflage..
or
Using a cardboard (index card will do) draw the desired camo shape then cut it. Put the index card over the area (give ample space between the surface and the index card maks-- 2 - 3 mm height would probably do) where the camo should be. This time you need to use paint from spray can. Spray over the
mask and you would get soft-edge camo.
BTW, try my suggestions on test areas before doing it on your kit...
Hope this helps...
Cheers