Refer to this PDF.
Dulux provide a free Revit add-in that creates Revit materials with RGB values matching their colours. Includes powdercoats and metallic colours.
You need to register to download it.
http://www.dulux.com.au/specifier/colour/bim#
In Revit, we often have to input RGB values for various color properties, such as shaded view colors for a particular material, or if you want a specific Paint color for a rendered material. To do this, you can use Paint.NET and the Color Picker tool - the resultant properties include the RGB values you need.
However, you may obtain a sample image of a material, but the color is irregular. For example, you scan in a paint sample and there is a color variation in the scanned image. Or perhaps you simply want to take a detailed pattern sample image and find out the average color of a particular part of that image.
Here's how you do it:
Download Paint.NET
Download Average Color plugin
Copy the DLL file from the extracted Average Color ZIP you downloaded into the 'Effects' folder, which is in you Paint.NET installation directory (for example: C:\Program Files\Paint.NET\Effects\)
Open Paint.NET
Open the image you want to find an average color from.
Make a rectangular selection.
Click on the Effects menu - Average Color
Now click on the Color Picker tool (looks like an Eyedropper)
On the 'Colors' palette, click the More>> button
The RGB values for your selected color are shown.
In Revit, input those RGB values for the desired color or material
Average Color of Selection forum thread
Plugin to Average Color of Selection - Paint.NET Forum
COLOR UTILITIES
CONVERT BETWEEN HEX VALUES AND RGB VALUES
Hex vaules are used for web and computer display. Sometimes the colour is only described in HEX.
http://www.yellowpipe.com/yis/tools/hex-to-rgb/color-converter.php
COLOUR SCHEME DESIGNER
Utility to identify complementary colors and other color combinations.