Drain covers the same color as pebbles?

Here's what PB is installing on my new pool being built. The plasterer did these yesterday and they should be installed today after they acid wash.
Plastering3_zpsi9y3mwkd.jpg
 
our main drain is a 2 foot diameter ring, so there was plenty of space in the middle to fill with the pebble. It's also totally flush with the floor so nothing sticks up.

But..it doesn't suck a whole lot. Anything with any weight just sits in the bottom of the collection ring.
 
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