Kindly state the Image spec (size, resolution). Filetype?

In InDesign, I believe the default viewing and printing of images is set at 'Low Resolution'. This can be altered (can't remember how as I'm not on my Mac now with InDesign).

What printer?

White outline turned gray? Did you check and see if your White is 'overprint'? 'Overprint' prints the top layer of color merged with the bottom layer.

yea.. I think you need to 'embed' the image file as well.

just do as it says regardless of whether he's an idiot or not... as long as you know that 300dpi is standard.

Sometimes, long long ago, I scan stuff at higher dpi but at 100% size, that way, I can scale up/down the image and have it sharper.