Frequently Asked Question
There are a few reasons for this.
First are custom shaders that modify default terrain brightness (PTA, Envshade...).
We suggest not to use any terrain brightness modifiers as they may result differences in airport satellite colors versus terrain. The airport and surrounding are adjusted for default shader values that comes with P3D.
Your Shaders folder is located at the path below
Local Disk (C:) ► Users ► You ► AppData ► Local ► Lockheed Martin ► Prepar3D ► Shaders
You may reset your shaders by removing the following folder and running P3D again in order to rebuild them or depend on your shader tools.
High latitude bug
There's another reason for this and it may be caused by lightning errors that are visible in such high latitudes and low sun angles.
It may result differences in lightning between native P3D terrain and custom airport terrain.