Software - Step through the code in Debug mode. Also, remember that the BlinkM is an AVR chip (ATTiny85). The source code for that is available on the BlinkM site. This makes it a black box as far as NETMF is concerned. As long as the command is sent correctly from NETMF, there’s not much else to debug without using AVR programming tools.
Also, in the future, if you have comments about a particular piece of shared code, please add them in the appropriate topic (the one created with the code link). This author is watching that thread, and will get notified when a post is created. This entire forum was created because of your request. Please use it as was intended, or at least, as I think it was intended.