On a recent trip to Sun Valley, several intermediate skiers (who typically ski Colorado) struggled with the terrain. Even the green runs seemed steeper than Colorado blues. I wondered if this was just in my head so I pulled up some topo maps to do a more scientific comparison.
The data shows that SV is much steeper. See the images below, the first two from SV and the second from Vail. Both maps have red shading on slopes steeper than 22 degrees (22 is the point at which many Colorado runs change from blue to black)
As you can quickly see, there are a lot more runs steeper than 22 at SV. Even the green runs College and Seattle Ridge have sections that are greater than 22. At Vail sections past 22 degrees are black (looks at the black part of Avanti and the black runs above Mid Vail. Blue runs at Vail rarely have even a hint of red.
Seattle ridge at SV:
River Run area at SV (including College run)
Avanti and Mid Vail areas at Vail: