It is odd that all your charts got changed. There is no method I can think of to change them all at the same time, accidentally or on purpose. You might be able to "revert" to a previously saved version (File->Revert to). I'd recommend trying it on a duplicate version of the document, not the original.
One thing that could change multiple charts is if they all included a row/column from the same table as a series in the charts. If you delete that row/column from the table, all the other series colors will adjust colors. They won't be "new" colors, they will just apply to a different series. If series 1 was blue, series 2 was green, and series 3 was grey and you delete series 2, series 1 will remain blue but series 3 will now be green.
If all your tables use the same style/colors, you can change one of them then redefine one of the chart styles based on it. Then it should be a simple click to change each of the others. I am assuming you did not use one of the built-in chart styles, that you changed all the colors. If you used one of the built-in styles and made no modifications, skip to step 5 below.
- Get one of your pie charts formatted the way you want it.
- Select it.
- In the format sidebar will be all the chart styles at the top. Right click on one of them and choose "Redefine Style from Selection". If you do the top left one, it will become the default for new charts.
- Select "all series styles" then "ok"
- Select another chart
- Click on that style and it should apply it to the chart.
- Repeat steps 5-6 for the rest of the charts