InDesign Shadow Transparency Issues
Working in Adobe InDesign is a bit tricky when trying to get a solid object but with a transparent shadow.
There are 2 issues here. First, is that a real shadow has a pixel data around it and you cannot clip a shadow as there are usually gradations around it. On a transparent layer there is nothing to prevent the shadow from having different opacities, but because the shadow is real in the photo, it cannot be isolated.
Second, InDesign doesn’t recognize Photoshop layers. The process of setting a shadow layer to multiply to get the white part of a shadow to go transparent works the same in Photoshop as it does in design, but since it doesn’t recognize those layers the process is to bring in both the shadow and object in separately, overlapping them and setting the shadow image to multiply. This is really annoying and there is no easy way to do this process.
This video guide from YouTube can walk you though it:
PNG With Fake Drop Shadows
Another option is to prepare these images instead as a transparent PNG with a fake drop shadow. How you would do this is remove the background around the product and then paint in a shadow on a transparent layer.
The issue is that a PNG is not a high resolution image and may degrade the quality, which is especially important when going to print. The other issue is that drop shadows rarely look perfect when painted in and it’s always best to stick with the real shadow if possible.
Create your colors in Photoshop first and bring it in
The other option is if the whole catalog is on a blue background for example, you could switch the background to blue in Photoshop, save it and then import it into Indesign after.
Strangely Photoshop and Indesign don't work as well together as they should in this instance. Illustrator/Indesign both handle layers and clipping paths differently than Photoshop and even though they are related programs, the layers seem to need to be structured in a very particular manner for them to work.
My recommendation is to perform your image edits in Photoshop and then bring them into Indesign to lay out. This is way you’re using the strengths of both softwares instead of trying to find work arounds.