If you are using spot colors in your imported graphics, it is essential that you define the same color in your page layout files. Keep in mind that your drawing software may name a color somewhat differently than your page layout software. (For example, Adobe Illustrator may name the color Pantone 287 CVC, while InDesign calls the color Pantone 287 CV.) Therefore, it is necessary to change the name in one file so that it matches the other exactly. If you fail to do this, each color will separate to an individual plate. Some page layout applications automatically add the correct spot color to the color palette when you import your graphic. If this happens, remember that even though the correct color was added for you, its name might be wrong.
The same rule applies to image editing applications if you are using spot colors to create monotones, duotones, tritones, or quadratones.