You can delete the colors you don't use from your swatches palette, manually, or by pressing the little arrow and choose 'select all unused' and delete.

Chances are that it still lists CMYK colors if you for example generate a PDF of it, but since you do not use those colors, that should not matter. You can always instruct your printer to ignore those plates, if they do not already, since there is nothing on them.

Also, the color 'Registration' (for crop marks and such) is built up from CMYK (or maybe the colors that are present in your document, I'm not sure).

Good call on deleting from the swatches palette--you can't delete black, (for which reason I hadn't tried the others), but they can apparently be axed. Thanks!

The registration marks basically defined in RGB thus present on all plates, but the registration swatch is a little bit special as it is also is on all spot colour plates.

Ah yes, on all plates. Didn't know for sure, but that was what I was aiming at with my 'or maybe the colors that are present in your document, I’m not sure' part.