The up and down arrows are there... they are just masked right now, I'm assuming cause I haven't reached row three yet. When I replace the mask with a transparent cel, the arrow is visible.
The palette I am using I think is from Hero's Quest, but if I remember, Brandon I think mentioned KQ's palette as a suggestion.
And it is thinner, because in script 15, the number of columns bit. Default is currently 5 and I changed it to show 7 items instead.
... the overall point though, is that the line in the scrollable inventory script, seems to be adding 4 pixels of padding for each item in a row... but the padding seems to be getting added to the end and not between the items like I would expect it to. Also, that would also probably be the cause of the highlight outline overlapping the items beside it. I didn't fix the padding between them, but my edit does remove all of the extra padding for each item and just adds 4 to it once to balance it out.