What is the Format of these images?
Check if there is any effect applied to it ? , Go to Object-->Effects
Indesign cannot edit the color of the imported images , like PSD , AI .... if these are the images which have been created in the Indesign then it's possible but you wrote you have the linked files hence I believe they are created in some other application and then imported in Indesign.
Can you provide screen shot and the 2 sample images.
Indesign cannot edit the color of the imported images
Not totally true. At least for black & white images or grayscale images ( e.g. TIFF) one could always apply a fill color.
@Sarah – so select one of those images with the direct selection tool (the white arrow) and see if a color swatch is applied in the color swatches panel for fill.
You also could set a black & white or grayscale image to "overprint". This might also be the case.
See this screenshot (German UI of InDesign CS5.5):
A screenshot of the selected image could help. "Swatches" panel and "Attributes" panel open.
Thank you, Laubender. That is exactly what I was looking for! Easy fix!