To build a nice nest it better to make one bigger room at entrance and a mail tunnel that connects the other rooms to each other like the pictures SteveUK28 showed.
To color your y-tong (i did it once) its best to take loam and put in a bit of water to make it moist, than paint your y-tong with it and if the loam dry's you have a nice ground looking y-tong. But it much of work so i stopped doing it

. Not harmful for the ants.