To do a multi-color effect in printing, print each piece separately so you can control when the color changes.
On the top brace, change filament at the 2mm mark to color the words.
On the gates, change at the 4mm mark to color the cross supports
On the uprights, change filament at the 8mm mark to color the torches. Or just leave that one and paint them.
To assemble, insert the top brace into the holes in the uprights, and snap down to secure them. Snap the gates into place in their hinges.