I have found a “Solution” and the cause to the issue we are experiencing. I assume this is something Epic would be able to fix in a short amount of time, if they so desire. The following thread that is covering another topic helped me solve the issue: How to turn off the mesh highlight for skeletal meshes? - Character & Animation - Unreal Engine Forums
The solution: When the engine is opened go to: Edit > Editor Preferences > Viewports > Expand [Look and Feel] and check [Highlight Selected Objects with Brackets].
This will enable Brackets around the selected object, but ensures that the colours will stay true in both the engine viewport and tilemap.
I am using version: Unreal Engine 4.18.2