Yes, quite clear.
Unfortunately, what you're trying to do involves using a brand new Special size that you will have to create (because the palette of special size monsters is determined by byte 2 in the table referenced in the post I linked above).
Doing so won't be too difficult, except that there are only two completely unused special sizes in the entire game, meaning you can only do this for two Underworld fiends before you have to get... creative... by which I mean destructive... by which I mean that you'll have to cannibalize some other monsters' special sizes in order to make this dream a reality.
In the past, I've suggested that if somebody wanted to do something like this, they could steal a couple of Octomamm's forms, since 8 is a little excessive, and I imagine few people see all 8 forms in a normal playthrough anyway. but regardless, you'll have to make a concession or two somewhere.
Aside from creating a new special size specifically for the new palette, you'll want all other graphical information to be identical to that of Kainazzo - same graphical pointer and aside from the palette same other four bytes in the special size detail table.
The post I linked above should contain all of the info you need to do what you're trying to do (even if it does miss some information we're only discovering now... you don't really need that for what you're trying to accomplish), but again, let me know if you need clarification on anything.
Of course, the other "problem" with this proposition is that it's going to require some hacking outside of FF4kster. Nothing that will make your ROM incompatible (I know, I've done it several times now in my hack), but since I think you've said before that you're trying to make a hack that specifically showcases the editor's capabilities, this might be something you don't want to get into... or you might want to whip up a new version of FF4kster that allows a hacker to edit the special size table (I know, that makes it sound so easy, huh?).
Anyway, that's all up to you. I'm working the closing shift tonight, so I won't be around most of the (EST) evening, but I'm home all weekend so if you have any questions, ask away.