So I have created my donut. It is grey no colors added no shaders added etc.
Now I am following some tutorials one is from Blender Guru I am in Part 4. Do I need to do what he is teaching here using nodes etc?
Meaning that when I export it to UE4 or Unity will the colors and shaders etc import and look identical to when you render it in Blender? or do I stop when I have just simply modeled it? and add in textures and shaders and lighting in Unity / UE4?
No the only thing that imports is the mesh. Colours of the mesh do not import.
Only thing that might be useful is if you unwrap a texture on a mesh. That will map to unity as long as you load on that texture.
You can do whatever you want on blender and then bake out a texture of the resulting colors and use that.
The video you’re watching explains how to set up the materials in Blender using its Cycles renderer, which does not render in real time. If you’re using Blender only for game-related purposes, completely forget about Cycles; it’s simply not compatible with Unity/Unreal or any other game engine.
Blender does have a game engine renderer, but it’s old and will be phased out in later versions in favor of a PBR renderer.
But yeah, create your meshes and textures in Blender, but when it comes to shading or lighting, do that in your target game engine. As far as I know, shaders/lighting aren’t transferable even if you were to use Blender’s (kinda sucky) game engine renderer.
Yes they do.
^^
I meant if he’s rendering it in cycles and expecting the subtle effects of an SSS shader’s colour etc to import
Thanks a lot everyone. 
Now I am going to create low poly trees and islands and mountains etc
Life sure is great
Not sure why you are asking about the UE4 workflow; these are the Unity forums. 
^ You would be amazed at the kind of knowledge people on this forum has.
You would be amazed at what knowledge the documentation contains.
https://docs.unity3d.com/Manual/HOWTO-ImportObjectBlender.html