I crocheted for about 15 years before I picked up knitting, so I tend to go back to what I know best!
If you are using the mattress stitch, one side will have seams, and the other side will have the seam allowances... so it will be ridged. If that's the look that you want, I say go for it! And if white goes with it all, go with that too! Since it's your blanket, you need to do what you can live with! :D