< So because those are not colored, would you then worry that they are also not flat, that they may have some small 0.5 angle degree from being horizontal?
yes but almost
they are not colored because they have not the same orientation than axis !

so just 6 colors
red, green, blue (dark or bushy...dashed...) verify if same orientation than axis
red, green, blue (ligth tiny...dashed...) or 3 other colors for being // a plan axis but not same oriention


(middle case don't exist in sketchup)
for middle case that must say that object must know original position :)
or used another same color (orange) who replace tiny red and tiny green that explain // at a plan X,Y