Material design docs actually seem to suggest you consider keeping the light grey of the main backdrop, but correctly use a z-axis difference denoted by drop shadow to indicate hierarchical relationship:
Or alternatively you can use several light greys, as Scott has already suggested - that usage is supported in the Material Design docs like so:
But in all cases the Material Design docs make clear that z-axis differentiation is crucial to establishing card/tile/section figure-ground and active/inactive relationships, all of which is denoted using the Material Design two shadows approach (one single direct light source shadow denoting overall depth and an ambient shadow when elements are close in the stacking order) and can clearly been seen in this similar scenario to yours example from the Material Design docs:
Note that the tiles in that image have an ambient-only shadow to imply that they float just one experiential layer above their container.
It's worth recalling that there are three major reasons to more closely hew to the published Material Design methods, specs and standards: first it meets the applicable standards and thus is less likely to face censure or negative actions from Google Play; secondly Google et al have spent immense time and resources to a degree which would be unsustainable for most smaller development entities to research, develop and test their design approach and tools - and the result, if you follow their methods, is attractive, simple, most crucially, clear, legible and effective; and finally, clearly following those design precepts helps make your app look and feel far more professional and well put together, regardless of the quality of your codebase - remember that the end user sees the UI, not your amazingly efficient, clearly commented and self-consistent code.
Hope that helps.