It’s quite usual to scan without photo pass so a lot of scanner session are only intensity channel… Sequoia don’t ask anything about that and cloud is color flat 
As you can see in attached image it’s useful to see a grey scale intensity colored cloud to work on it. Now my solution is open cloud on CloudCompare, use intensity channel to color cloud, and than save it for Sequoia.
I know, this is no a critical issue but I think is easily salvable by a “import dialog”.
We have an Import dialog for formats that require manual channel remapping.
Loading PTX does not require the dialog though, because the channels are clearly mapped.
The actual solution that we have planned (but not implemented yet) is to allow the Color channel of any point cloud or mesh to be set to any other channel.
For example, setting the Color to Intensity would dynamically produce viewport colors based on the Intensity imported loaded the file. If a Normal channel exists (it does in some of our PRT files coming from 3D applications, as well as in all Meshes), setting Color to Normal would colorize the point cloud based on the Normal vector’s direction. Same with TextureCoord channel etc.
Obviously, the ability to set the Color channel to a static value (e.g. White to remove the Color channel data), the option to rescale and clamp the values etc. would also be provided.
Thank you for the feedback and for your patience! 
In our next build, if a point cloud does not have a Color channel, then we will show the grey scale Intensity instead.