How to make white whip cream?
Heavy cream can vary in color depending on the feed given to cows and the breed of cow.  Where I am, it's rare to find heavy cream that's very yellow, so my whipped cream usually is white enough that it's not a problem.  (It's not generally bright white, but not noticeably yellow.)

If you can't find white cream, as Joe mentioned in a comment, try white food coloring.  I've usually seen it in paste or liquid form, but powdered versions exist too.  If you can't find it in a grocery store, it's available online (and your local bakery might be willing to sell you some).  I've never used it for whipped cream, but it's the common remedy for icings when you want them to be bright white rather than the off-white/light yellow you might get with a traditional buttercream made with a lot of (yellow) butter.