One of the earlier elements of the LEGO® Modulex system was the architectural profile brick. There were several sizes and the details are interesting to review. One style of the brick had a stud on top, an open side, and an open bottom. You can see each of the three sides has a different texture: smooth, shutters, or vertical bars. There are 2 different height versions of this style of profile element: 4 brick height and 5 brick height.
The other main type of profile brick is horizontal in orientation. There are 4-stud, 5-stud, 6-stud, and 7-stud versions. These bricks have a different texture on each side (so, two options).
There were four colors available: Black, Brown, White, and Grey. When the LEGO® Modulex direction changed from architectural rendering to plan boards, the element was no longer available. Notice that the studs have the earlier LEGO® marking (later bricks have M).