Problem - yellow shapes appear when I click any object

Just starting with Unreal Engine, but I REALLY need to solve this before I get going.
Any object I click on brings up 2 yellow copies of it, 1 on it’s left, 1 on its right. This makes it impossible to see what I’m doing - especially if it’s a large object like the sky, when basically the whole scene turns bright yellow.
Help much appreciated!