Hi Della,
I'm afraid we don't support syncing colors like that. Depending on how your user filtering works, you might have to do different things. For example, if you're using the Google Charts Controls, those will actually remove the row from the DataTable that the chart sees, so there isn't any sensible way to reassign the colors for things appearing after the series you want to hide.
However, if you have a custom filter, then there might be a possible solution:
On a line chart, you can hide the series by changing its visibleInLegend option and setting the color to 'none' or 'transparent', and on the pie chart, you can hide a series by simply setting its value to 0. This automatically removes it from the legend as well.