Excel uses a standard palette of colours, but it can be modified. These modifications stay within the workbook where they are changed.

You can reset the colours back to the standard palette in the "Tools > Options" - Color tab. You can also adopt a custom palette from another workbook.

If you copy a worksheet from a workbook where there is a custom palette, the worksheet will comply with the palette of the workbook where the worksheet is pasted.

Cheers,