Rolled hem napkins

I am new to the board, but have been sewing for 40 years.  I have a Baby Lock serger but have not used it for a rolled hem since my daughter's senior prom nine years ago!  A friend has asked me to help her make rolled hem napkins for her daughter's wedding.  When she bought the fabric, the people at the fabric store she went to told her she only needed one cone of thread in the color of the napkins and could use white for the other two threads since it wouldn't show.  She was greatful because she is making napkins in five different colors and didn't want to have to buy 15 cones of thread.  When I try the rolled hem stitch I can see all three threads.  If I adjust the tension, I can make the lower looper thread almost  disappear, but not entirely.  Is there a way to do a rolled hem such that only the upper looper is visible?  If so, how do you achieve that?  Thanks so much for your help.
Meg

I tried on my Babylock, and I can't do it either.  However, I think the lady at the store may have been smoking crack.  You shouldn't have to adjust the tension so much, I would just invest in the thread.  Maybe just one more spool of each color?

Thanks, at least I know I am not the one who is crazy!   Thanks for your help.
I had her buy a second spool of each of her colors and now 200 napkins are done and ready for next weekend!