As you will notice, there are slightly different shades of black; even though the "black ones" are all black and OEM. The camera flash, background color, and distance from the camera lens will also affect the color appearance. Many - but not all - gaskets were made with printing on one side and not the other. During the decades that this gasket was (and still is) sold by Stihl, they certainly used different gasket vendors and different materials (whether due to durability or profit margins). You'll also find that packaging (and labels) varied by date, distributor and region/zone.
A prime example; looking at the cylinder base gasket in your kit; it's olive green in color w/the supplier printing on it. That 1118 029 2306 gasket was also sold in black/gray, two-tone green and white, and olive green. All colors were sold by Stihl and all were/are OEM.
Lastly, here are two pics of an 1121 007 1050 gasket/seal kit. As you'll clearly see, this is an OEM Stihl kit, however, the gasket colors are lime green; far different than the color in your kit. Does that mean that your kit is fake, or this one is? Of course not. It simply means that Stihl used different colors and shades of gaskets. This is the same lime green, by the way, that is shown in my previous photo (on the right/bottom right side).
Point being, you can't assume a gasket is or is not OEM by the color shade.