The LandXML Schema does not support Color as Standard, the output from TBC does have an extended LandXML output that does transfer the Layer Colors as you have highlighted, however Connect does not support those Colors in a LandXML file (because it is non standard and because it is managed by a different group ...).
If you round trip output from TBC and then Import back into TBC the Colors will work.
When you import a normal LandXML, if you use the Import command rather than Drag and Drop you can set some parameters on Import that are used to Layer the data from the LandXML - normal LandXML also doesn't support layers - so we allow the user to pick up on the Name and Description Fields and use those for layer names as a poor man's alternative - this at least splits the LandXML onto Layers that are more useful than everything on Layer 0 and a maunal sort through the data. The last used settings are remembered so after you have imported one file you can use Drag and Drop thereafter.
If before you import a LandXML file you can set up all the Layers with Colors and Linestyles etc. then on Import the data is directed to the existing Layers and pick up the Layer Properties for Color and Linestyle etc. That means having a Template for the data coming from a specific Engineer and relying that the Engineer will be consistent from Project to Project.
Hope this helps
Alan