Christine, I had an idea that might make your cables stand out more: why not carry an extra piece of black DMC Pearl Cotton along with the Ragg yarn, just in the areas of the cables?
You know how folks knit with extra thin "flag" or "eyelash" yarns along with the regular dk or worsted?
Well, you could do this with any thin black yarn! It could make the cables a darker shade than the sweater itself. You would pick up and knit with the black Pearl Cotton at the first stitch of the cable...and after knitting the last stitch of the cable, drop it, let it hang in the back...and continue to the end of the row with the Ragg only.
Then...when doubling back and knitting the wrong side...when you come to the black Pearl Cotton dangling at the beginning of the wrong side of the cable, pick up and knit with the black Pearl Cotton til the end of the cable, then drop the black Pearl Cotton and knit to the end of the row with Ragg only.
Get what I mean?
I don't think the black Pearl Cotton will significantly increase the thickness of the cabled area...but I think it definitely could add some depth of color to the cables and make them pop.
Or, really...any thinnish black yarn would work, too.
It's an idea.