Beside the fact that there is a slight syntax-error by missing an closing brackets for match() and one too much for the pick() your variable needs to return the same structure as if you would write this manually like:
pick(match(Item, 'Item1', 'Item2', 'Item3'),red(),Yellow(),black())
which your getfieldselections() don't return because the list-values won't be quoted. This meant you need to use a different approach for example:
pick(match(Item, '$(=concat(distinct Item, chr(39) & chr(44) & chr(39)))'), red(),Yellow(),black())
Further I suggest to apply this kind of color-assignment within the script like: Colors in charts.