When a chart is rendered, it utilizes the charts palette to draw the different elements. This means that each bar, slice or line is going to have a color applied in the order of the palette colors.

When a filter is applied to a chart, the chart is rendered again, which reapplies the colors to the chart in the order of the palette.

Here is an example:

A chart with no filters applied, where the 'Email' category is a light tan color. That color is applied because it is the 4th color on the palette.

After the filter is applied, there is only a single bar per month. This results in the first color of the palette being applied to the 'Email' bar.

If you need to keep colors consistent, whether they are in the filtered or unfiltered state, then you will need to apply conditional colors to the chart.

The following is an example of the conditional colors applied in an unfiltered and filtered state.

In this example, a conditional color has been applied to the 'Email' category, which makes the bars with that data styled with a blue color. This is the chart drawn when no filters have been applied.

This is the same chart after the 'Email' filter has been applied. Notice how the bars remain the same color, because of the applied conditional colors.