baffling image question

[obair81 at comcast.net]

In a manual that I am writing, I have a tiff with some blue Ethernet cables that look purplish in spots.

I did some "painting" on the tiff in photoshop to add a blue cable, since the cable setup changed after the photo was taken.

The tiff is from a high-quality photograph of our product. 

I have used high-quality photos from this photographer before, without trouble.

I am told that our printer is working ok.

This is a new one on me.  I am the sole writer/graphics person here, so...

Thanks for any help.   

best,
Paul