From the first day i noticed the 3D Manipulator can be bad visible.
Someone else confirmed the on the scene the work on.
Normal you see it like this.
Perfect visible bright colors.
But as soon the 3d manipulator is going inside the object, the store get complete different. many times it's very hard to see where the arrows are. And we have no option to move by keyboard. This start to get a problem when you build more. On this example i scaled the barrel up so the whole 3D manipulator is inside the object.
It looks bad but on my screen it's almost invisible, The 3D Manipulator need to be much more visible if it's inside buildings. It also depends on what side you are.
ADD: Extra picture to show the difference. on small object when it's inside and outside.