Color Converter is a Coda plug-in that allows you to quickly convert Hex colors to RGBA or regular RGB, and RGBA and RGB to Hex.
Download the file and put the plugin in your ~/Library/Application Support/Coda/Plug-ins/ folder.
To use it just highlight a color declaration you want converted. Be sure to get the whole thing including the #/rgba(/rgb( at the beginning and the ) at the end, or you’ll get some left over items in your converted colors.
Now just choose the conversion you want to perform from the Plug-ins menu under Color Converter. And viola! Your old colors are converted to the new format.
If you converted to RGBA, you will note that the cursor is inserted at the point where you will enter your alpha value. Just type a number from 0-1 and you’re done.