Be aware the the plexiglas or acrylic will scratch easily. You’d be
surprised how easily.
Another, and I think better, way to accomplish the same thing is to
take a piece of thin glass and paint it on one side with the color
of your choice. Set the piece to be photographed on the UNPAINTED
side of the glass. I like to use non-glare glass as it gives a more
subtle and less distracting effect.
Additionally, you can suspend the piece of unpainted glass above a
colored background of your choice (I prop mine up on bricks) for
various effects. There’s no limit to the variations one can achieve
this way. One thing you will learn very quickly: When photographing
shiny objects on black backgrounds, the black is reflected into the
metal and stones; AND, because balck is such a poor reflector of
light, the bottom parts of the image need to be lit separately to
reveal adequate detail. The image you spoke of shows this fault.
Nice, but a neutral background would let light reflect up into the
bottom portion of the piece, improving the detail significantly. Try