Open the picture in the graphics program right click on the default background layer and select duplicate. Click on the filter tab at the top of the page select blur and then Gaussian blur change the value of the pixels in the window that pops up put 20 to start but the number can be as necessary
They are referred to as neutral colours.
I believe the answer is Post and lintel construction. (Columns).
I don’t think domes were invented.
Flying buttresses were invented for the Notre Dame Cathedral in France
Towers and spires are not likely.
I hope this helps!