Can I use white rice flour instead of brown rice flour?

Yes, you can. The brown rice flour has a slightly nuttier flavor, but white rice flour will work just as well in that GF rhubarb, lemon and almond cake recipe.

That looks like a wonderful recipe, by the way. The rhubarb in our community garden is flourishing - growing like a weed, in fact - so I'm tempted to make this for our GF guest who's coming to stay next week! ;o)