I was at the LFS the other day and I noticed that all the Perfecto (marineland) tanks that have black silicone only have the front and back edges done in back. the bottom is done in clear..I was surprised at this. seems a bit sloppy to me, but it must be cheaper to do.
I thought when you have a tank made with black silicone, the whole tank is done in black silicone (my Aqueon was), not just the parts you can see..
I guess there is no issues with the black bonding to the clear where the side seams meet the bottom seams.