Surface color only has to do with 3D views. Fills in 2D views have a foreground and a background color.
But, in this case, it appears that your elevation has 'sun shadows' enabled - and a 25% gray (or similar) fill set as the sun shadow fill. Just disable sun shadows for your elevation... or if you want shadows, change the elevation's sun location to illuminate more of that elevation. These settings are all part of the elevation (or section) tool settings for the view you're showing.
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