You used Copy/Paste, right? Placing the file won't bring the swatch. If that's correct, go to Preferences > Clipboard Handling... and uncheck Prefer PDF When Pasting, ten coopy and paste again (I had to re-copy to get it to come in correctly after changing the preference).
One more thing. Change your Illustrator Document Color Mode (file menu) to CMYK before copying your element.
I seriously doubt that RGB swatch has anything at all to do with the gradient. It probably cam in from Word or some other application. The Blue Steel gradient is already CMYK, and when pasted here it creates a new "New Gradient Swatch" swatch.
I experimented with this, using new documents. It wasn't the swatch, but the document mode.
When the source Illustrator document was RGB, it didn't paste correctly, and it added the r0g0b0 swatch. When I changed the Illustrator Document Mode to CMYK and then copied the same gradient element and pasted it into the same InDesign document, it worked correctly.
(with prefer PDF when pasting unchecked, as you suggested)
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Very interesting. Sounds like a bug, but I'm not sure if it's in ID or Illy.
Thanks for the quick replies.
Not at the same computer at the moment so cant experiment but I had already unchecked the clipboard Prefer pdf.
The box and its gradient were both from Illustrator, the gradient is one of the ones that is supplied with Illustrator.
Will change color modes and report back.
Changed Ill to CMYK and its fine, all color stops etc.