When saving your files. They should always be saved as CMYK files.
Files that are not saved correctly can sometimes lead to color issues. Since RGB (what you see on your monitor) has a different overall color gamut range than CMYK (printer colors). It makes sense and is fine to create your files in RGB mode, but when saving your final file create a CMYK color mode version to submit to us.
Most colors match better between the two color modes. This example was used to show chosen colors that are well beyond the CMYK gamut range.
Menu Bar: File > Document Color Mode > CMYK Color
Menu Bar: Image > Mode > CMYK Color