In the Vector Tile Style Editor, you can actually see that the "two colors" is due to the Land/Not Ice layer showing trough the water layer, either because of transparency of layer blending. Not all basemap styles include this layer, and as with any layer in the vector style editor, you can remove/restyle it as needed.
The boundary gap should be resolved in our December release (~16th of the month). Thanks for the comments.
In addition to Esri Community, we have basemap, geocoding and imagery feedback services where users can add comments on the map and get items fixed: https://www.arcgis.com/home/group.html?id=e796c4f5b27b431a804184fc51d10b40#overview