the difference is of physical nature. VH is only the return of horizontal waves which were emmitted vertically. Its proportion and occurrence is smaller in most cases:
We have had some discussions on this:
- Difference between VH and VV polarization
- Sentinel 1 (VH vs VV polarizations)
- VV and VH Polarization
- Sigma nought values change working with Sentinel-1 SLC
- Difference between radar channels
What is often done for RGB composites is that you take the VH multiple times, e.g.
red = VV
green = 4 * VH
blue = (2*VH) / VV