If they are truly SI1/2 and not I1/I2 there should not be any eye visible difference. There would be a LOT more visible difference between singe and full cut.
It's important to remember that melee stones are graded by the seller- as opposed to GIA.
Therefore the answer really depends on the way the person grading the diamond did their job.
Also very important is how well cut the stones are.
Properly graded Si1-2 stones that are super well cut will look far better than poorly cut VS stones