I love the combination of yellow and Yuzu Cybilla. It smells uplifting and bright. You could pick Champagne or Ginger Ale for your second color to give the soap a bubbly note.
What I learned in class is that
most two color combinations look great as long as there is enough contrast between them. We were told to pick two colors we didn't like - then did swirls with both colors. Surprisingly nice results on all of the combinations, just not what I could have imagined or planned in my head. So pick another color that you like and try them together.