Much of landscape photography is being in the right place at the right time. Some photographers know these places and times based on their extensive experience. The more knowledge you have, the better the chances that you'll be in that right place at the right time.
In this video from Dianna Cowern (aka Physics Girl), she explains not only that white rainbows are a real thing, but also how the different kinds of rainbows occur. You read that correctly: there's more than one kind. There are regular rainbows, circular halo rainbows, white rainbows, sundogs, 22-degree halos, and even an optical phenomenon called a glory.
Once you know what causes these different kinds of rainbows, you'll be better prepared to watch the weather conditions and be able to be in the right place at the right time to photograph them.
There's always a bit of luck involved when it comes to weather, but I've always believed that if you know how something works, you'll be much better off when it comes to working with it.
Cowern also covers some basics about refraction, which can always be useful information for anyone that works with optics. Check out the video above, and you might just learn a few things.