I used to own various L BLUE (navy) dresses but I have retired most of them. I still own one but it is not really a "blank canvas" in the way several others I owned were.
The two most useful ones I owned were a Ralph Lauren knee length cotton knit shift dress that I could wear on its own (sleeveless) or layered over or under, with tights or without, etc. It was extremely versatile. Pretty much a 4 season item -- though I wouldn't choose it on the hottest or coldest days. A real workhorse and great for travel. Dress it up with jewellery and footwear and a wool coat or trench; dress it down with a chunky sweater over top or a tissue turtleneck or shirt beneath, a denim jacket on top, sneakers, tall or stompy boots. I think you'd get a ton of wear from a dress like that in a core neutral. It works for people with a mainly classic style.
A David Meister sheath, dressier but with a modest yet flattering neckline so it could be used at a funeral or other solemn occasion, but the neckline and cut made it date-night worthy.
If I found a contemporary midi length version of one of these I'd probably snap it up. But I haven't found one. So I do without.
The current navy dress (below) is much more limited in function and season, but still a great dress. It would be similarly limited in any neutral or colour, I think. Cotton poplin is nice for summer but not warm enough in cooler weather.