Create a new symbology and select color from color palette, "More Colors..." (RGB) or new button "Pick Color" (se attached picture). Pick Color should activate all pixel on screen and color on pixel you select with mouse should be used. Pick Color should work like Pixie from Nattyware, read more on http://www.nattyware.com/pixie.php
Then is this useful?
While conversion from other CAD och GIS application you have to convert data and make symbology like the source. Start source application together with ArcMap, create symbology and Pick Color from source application.
You have got a design guíde in pdf-format from a departement och standard organisation. Open pdf together with ArcMap, create symbology and Pick Color from pdf dcoument.