I'm not sure why SW1BROWN is yellow-tinged (source port with coloured lighting); ordinarily it is the same grey colour switch as the others, being the same texture patch. Also SW#STARG uses this switch in Doom 1, although it has a different switch and background in Doom 2 because why should the same texture name mean the same texture in both games, eh?
I'm kind of torn about writing this next bit because you may know it already, but I'm not sure why someone who knew it would write what you did. All Doom textures are assembled from one or more underlying texture "patches". This saved considerable space in the IWADs when, to give a very obvious example, they wanted "that same wall, but with a switch on it", or to use the same switch on more than one kind of wall. Hence it's not surprising that these switches look the same; it's also easy when editing to put any switch you like on any wall (so easy I'm slightly surprised Doom Builder doesn't do it, and maybe it does).