Hi there,

This is a rendering effect and usually this is more evident with the white color, because the gray color that you see is actually the white color with shadows. Also, in Punch, the programs apply the textures / colors in tiles from one corner to the opposite corner of each wall segment, for this reason, the shadows of the two parts (lower and upper) look different.
In order to set the desired effect, change the lighting settings.

Now regarding the differences between the trim and the walls, this is due the size / height of the segments.

Hope this helps.