new Juvenile redtail giant gourami, has a black dot ? Gravel color ?

I have a large giant gourami and I run the tank with a bare bottom. Do other do this or do you use gravel ? I have a wet dry system for filtration.
I recently acquired two Juvenile red tail giant Gourami's (4-5") for a different tank. They have a silver underside and a black dot on the rear. I have not seen
this before, have others ? I with these new guys I was thinking about gravel color since the are pretty dark. Any suggestions ?

Regards,
Bob.

both of them have this black spot, do you think they are not red tip GG ? I had assumed there was only one species of red tail GG. My big boy must be 26 to 28",he is the typical grayish color. If there are only 4 different types of GG, what are the others ? I assume an Albino.

ok, I did know they were different, I have read there are 4 types. I know of two. Is this a correct statement or fishlore ?

Do you use a gravel base or a clean glass bottom ? I have run bare glass for many years, I use a small power head to stir up the bottom. I was not sure if the fish need to poke around the gravel or the gravel is just for looks.