Details
If you execute export_ugdwgimages.exe (found in the %UGII_BASE_DIR%\NXBIN folder for NX11 and later release) in a command prompt without arguments you will get this command help
C:\WINDOWS\system32>"C:\Program Files\Siemens\NX 12.0\NXBIN\export_ugdwgimages.exe"
You must specify a part name with -part switch
export_ugdwgimages
-u : username (iMAN account)
-p : passwd
-pf : file containing passwd
-g : group name
-part : Part name in NXMGR style @DB/<item>/<revision>
For non-default domain,item value will be MFK id.
e.g. @DB/<%#MFK#%,=item_id=001,object_type=SupplierPart,supplier_code=x>/<revision>
-all : Generates CGM/PDF images for all the drawing sheets in partfile.
-sheet: Generates CGM/PDF image for the drawing sheet specified
-text: Text output mode specify either "text" or "polylines"
default is specified by a customer default for CGM export.
-retain_sheets_in_os: The CGM/PDF files generated will be kept on
the OS and not sent to the PDM system
-bom_file: Specifies a file to list the CGM/PDF files generated.
Required when -retain_sheets_in_os is used
-pdf: Generate a PDF
-nocgm: Supresses generation of CGM files, if the -pdf switch is present
-pdfcolor: color to use for PDF "displayed", "part" or "monochrome"
defaults to monochrome
-raster: "on" or "off" default is on
-shaded: "on" or "off" default is off
-sort: "alphabetical" or "numerical" default is order created
-case: Preserve case
So it seems that to get a color pdf the options to be used are -pdf and -pdfcolor (the latter with the options listed there, "displayed" or "part").
Instead you will realize that the -pdfcolor (=displayed or =part) does not work at all and the PDF export always defaults to monochrome.
Solution
Actually there is an error in the command help for the export_ugdwgimages.exe tool.
The correct option to get a color pdf is not -pdfcolor but -color, so it will work if you use the -pdf -color=displayed (or =part) combination.
Hardware/Software Configuration
Platform: all
OS: n/a
OS Version: n/a
Product: NX
Application: GATEWAY
Function: PDF
Ref: 002-8013896