It doesn't appear, in this panorama, that we are anywhere close to the Colorado River. In fact, we are 300 yards away from the clear green waters. We can easily see the cliffs on the far side of the Colorado River from here.
We are situated in the very lower reaches of South Canyon just before it exits onto the outwash delta and then to the river. The Green Shrub in the distance is an invasive Tamerisk that has grown on the sand dunes of the delta.
This slot is in the Redwall Limestone formation. As we can see, the limestone walls are really gray and white. Those are the true colors of the Redwall Limestone. The name Redwall was given because in most of the Grand Canyon, this layer of Limestone is coated with red silt and clay from the eroded Supai layers above it. The red silt and clay wash down from the formations above and coat the gray and white limestone and make it appear red.
You can view this and many other panoramas of the Grand Canyon at GCPano.org where you will find more detailed descriptions along with topo maps and interactive movement from one panorama to the next.