I got given a PDF map document today from a client who wanted me to use a colour theme similar to the advertised material. The challenge was working out exactly what that colour is. I took a print screen of the map and saved it as a bitmap. Then I opened the image in Microsoft Paint and used the
color picker tool. Then clicking on
Edit Colours button will throw up an interface with the RGB value.
Punch the RGB value into ArcGIS under Symbology and viola, you have the exact color match.
Althernatively you can do it a longer way... sending the image to HTML5 Colour Picker:
Both methods work depending on whenther you have access to image editing software.