Hi,
Yup -that's why I'm suggesting taking the aspen out of the equation for now - if we can simplify it but get it working well before you bring him home that is by far the best way to go.
Unless the tub is thicker on the bottom than the smaller ones it shouldn't be whats causing your immediate problem. Smaller tubs are better for more nervous snakes but you can try it with this size and see how he deals with it after the initial settling in period. Just keep in mind a smaller one might be needed if he won't settle down and eat well.
I use coloured newspaper all the time without any problems.
I have never had much of a problem with it staining the undersides of the snakes either - but then again it might be more noticeable with a BEL or albino.
Each substrate has its good and bad points - I personally like the fact I can't spot clean with newspaper. It's either clean or it isn't - and if it isn't I clean it.
dr del