Tubes on black backgrounds show themselves completely and can be used with any color background.

Tubes shown on white backgrounds either don't look good on black or are best left that way.


I put the one Sand Dollar on white to show the inner circle's slight (dark) shadow/flaw and those around the edges.
The one Sea Coral is on blue because it has white and black edges that would have gotten "lost" on a background of either color...this way you get to see it as it is.

All of these were tubed from pictures I found on the internet years ago.