The command SET_PART_COLOR is specific to parts and the great thing about parts, as opposed to something like faces, is that you can see the path to the part in the structure browser. So if you have a part that you want to change the color of, you can use the command and pass in the full pathname of the part, in double quotes, as a parameter.
Assume you have a top level part named "Part1". Its full pathname is "/Part1". The command you would enter in the command line to change the color of this part is:
SET_PART_COLOR "/Part1" :RGB 0.2,0.5,1.0 :done
If you wish to make the part's name a parameter within a LISP macro then the code would look something like this: