If you use the color gun and edit the default yellow to a new color you like it changes all default colors to the new color without doing any painting as well as all new items built will he in that color.
Problem is some items still come out as yellow. I have found the MK4 conveyor belt and wall gate in normal play do this. Everything is white except the conveyor and gate. If you use the F key to delete something and highlight that yellow object its color changes to the new one. The gate remains the new colour after being highlighted but the conveyor returns to yellow after loading the game.
Its killing my OCD man