Both pieces 14418 and 22890 appear in quite a large number of sets, yet they are only available in light- or dark bluish grey. The reason I find this strange is that in many cases, they do NOT match the local colour(s) of the set they're in.
Is there a known reason for this? The only one I could think of is that perhaps the material properties for other colours might be slightly different (e.g. not enough or too much friction when connecting the two pieces), but I would be rather surprised by this.