What is the strip called on the rim that when you push the brakes on? I have a fixed bike and I bought it a new front white deep v rim that doesn't have the strip on it for the brakes and when I used it the wall gets dirty from the brakes. Can I buy the strip or is it suppose to be like that normally?
The part of the rim you're talking about is a brake track or braking surface (the silver colored thing in this picture): which is where the rim brake is supposed to make contact with.
These are a part of a particular rim's design and are not available to be added after market.
You should check that your rim is indeed intended for rim brakes (not all rims are) and if it requires any special pads. You can do this by checking with the rim's manufacturer. If its not intended for use with rim brakes, I would suggest getting a different rim (as using them with rim brakes may lead to rim failure, which is bad).
Note that even if it is intended to be used with rim brakes, it may not provide as good braking as a rim with brake tracks and you may want to clean the braking surface more often.
Just to expand on @Batman's excellent answer...
Rims properly designed for rim brakes will have sufficient thickness of material to withstand wear from the pads.
It's not uncommon for track/street rims to be 'unmachined' like yours. Most of the time the downside will simply be dirt / paint wear as you have experienced, but bear in mind that many deep rims aimed at the fixed gear market may well assume brakeless riding, and running rim brakes may compromise their safety before too long.