I will show sewing next week, but I want that to be a useful, informative blog and those take a while ...
Anyway, because these tulle skirts are skirts and not tutus, they have a solid underskirt lining, so you can't see through them.
You can see on my samples no lining shows.
But, the design department at Simplicity thought the lining should be the same length as the skirt. And, if you look at the pattern envelope above you can see the lining at the back of the legs of the pink skirt.
SO ... this is a design choice and you have options.
This is an effect I like a lot, so something else to think about. Actually, it would be fun to maybe have 3 different colors.