As IceCreamEmpress says, an agent could care less. You can tell them, certainly, but it's up to the publisher's Sales department and Art department to determine the cover. You're quite right that the cover is very important--especially for a debut novel.
Here's what I would do in your place:
1. Look around the bookstore in the paranormal romance section.
2. Find a cover design that you DO like. It needs to be a USA Today or NYT author.
3. Find a color scheme that is different but interesting (again from a USAT or NYT author).
4. Choose a pen name that will have your book appear at EYE LEVEL on the bookshelf. That would be the second or third shelf down from the top. Trust me, this will
excite the Sales department!
Once the book is accepted for publication and you're chummy with your new editor, you say something like:
"Oh, BTW, I was thinking about the cover design. I really like the design that [insert author name] had on [title of book and series]. But the colors are probably wrong for this book. The colors on [insert author name] on [title of book and series] would look great, though! Is there any chance of doing something like that?"
Obviously, Sales and Art would both love nothing more than to grab the readers of Famous Author #1 and Famous Author #2 for your debut novel. It's almost a guarantee you'll get something close to what you want.