They do work, it’s just a bit of a bug (I can’t think of a better word for it) in your code. If you shake the iPad while drawing (using your code), it just changes the width to 3 then immediately back to 35.
I tried the code below and it worked fine (although it wouldn’t be very good for a drawing pad).
Image of what the code did
(Please excuse my lazy image editing. :P)
This post is probably horribly worded, sorry.
I guess the set trail width and set trail colour blocks are kind of unecessary, though – I always seem to use variables instead.