Ok, so you have PMS 7545
Which the CMYK breakdown is
C-23
M-2
Y-0
K-63
You applied a drop shadow of 40% black, and it's set to multiply. This multiplies the base colour by the blend colour. In this case the base colour is, in theory, mostly C and more mostly black at 63%. This then feathers, as the drop shadow is set to 0, if you set it to 100 you will see a gray bar. If you multiply any colour with black it produces black, and conversely if you multiply any colour with white the colour remains unchanged.
What's happening here is exactly what you asked for. It's multiplying a gradient of 40% to 0 x 63%.
You can try to darken your Drop Shadow Colour by creating a Rich Black of 30 30 30 100, and applying that.
But you're basically applying a drop shadow with almost the same values as the background, hence why it looks the same.
You will need to adjust your Transparency Flattners... check out this page
Something I read a while back on the subject its taken from the Adobe Live Docs Page:
Specify a color space for blending transparent objects
To blend the colors of transparent objects on a spread, InDesign converts the colors of all objects to a common color space using either the CMYK or RGB color profile for the document. This blending space enables objects of multiple color spaces to blend when interacting transparently. To avoid color mismatches between different areas of the objects on-screen and in print, the blending space is applied for screen and in the flattener.
The blending space is applied only to those spreads that contain transparency.
Choose Edit > Transparency Blend Space, and then choose one of the document’s color spaces.
Note: For a typical print workflow, choose the Document CMYK color space.