Are you, by chance, a former Nikon user like me? LOL
There's a line on the cap that must be at the top of the lens mount to go on, unlike Nikon that allows it to go on from several positions. I've taken a silver Sharpie marker and gone over the line so it's easy to see when I go to put it on. Even then it's still frustrating after 20 months post-switch.
Are you, by chance, a former Nikon user like me? LOL
There's a line on the cap that must be at the top of the lens mount to go on, unlike Nikon that allows it to go on from several positions. I've taken a silver Sharpie marker and gone over the line so it's easy to see when I go to put it on. Even then it's still frustrating after 20 months post-switch.
This is the same for the lens back covers as well on the new RF lenses. They are "keyed" in one spot only. On the old camera body and aft lens caps the lens cap could be rotated until the cap engaged with one of three positions corresponding to the flanges on both the lenses and the camera body. That was easily done without looking at the older EF mount. The newer RF mount is keyed in one location only for the caps. This is not an improvement from the "user perspective" IMHO.
This has been a problem for me with the RF lenses. As I have aged I find it harder to discern darker shades and colors. I find the red mark on the RF lenses to be kind of a dark shade of red but the lens barrel near the rear of the lens is sort of a pewter tone or silver grey and for me the red blends in. Also as mentioned the lens and body caps can only be attached in one position. I took some bright red nail polish I found in my wife's miscellaneous makeup drawer and painted red in the notch on each lens cap making it much easier to get them on, usually I am changing lenses for a reason and hate having to fiddle with getting the cap on so this has helped me speed it up.