Titanium Dioxide works best. I personally don’t find that kaolin clay does an adequate job making the soap white. Also using light oils/butters help as well. I too use 1 tsp ppo.
Felicity, I really like using titanium dioxide and like @shunt2011 use light colored oils. The very first time I used it, I did get glycerin rivers (and then learned a whole lotta stuff from this forum!). Now when I use TD, I soap at a low temperature and use 33% concentration of lye to (lye + water). Have fun and post photos!