As I say in the description of th sideart (in the Illustrator file), I'm not sure of the colors, but I doubt 3dmacman or Zorg (the original authors of the other sideart version and not mahuti) knew which colors were accurate. There are actually different color schemes used. I have collected dozens of sideart pictures and there seem to be 2 color schemes. The original one (on the old and damaged cabinets) and a new one (taken from restored cabinets). Apparently Twobits does not use the original colors, or the original paint changes color over time. This is most apparent in the dark green areas in the ribbon on the sideart. In the original artwork you can see clear dark patches, but the restored artwork hardly shows these. The logo seems to be out of one color too in the restored artwork.
I redid the sideart because the baseimage 3dmacman and Zorg used was very hard to use and at some points incorrect. The colors are too dark (especially compared to the original artwork), the image is warped (bottom is skewed to one side and is tapered inward) and the top logo is taken from the flyer instead of from the sideart (with stars inside the logo). The bitmap baseimage was apparently worked on a lot thereby damaging it's use for vectorizing. Also the images I used where much higher res, so I guess there will be some more detail in there as well. On the other hand, the artwork I used is from a "class of 81" and allthough I tried to correct differences between them, there might be small differences to the original. But all in all I feel my version will be more accurate

If you have Illustrator (or download a 1 month trial) you can easily change the colors though. Just click on an item of the color you wish to change. The corresponding "color swatch" is then selected on the right (or just click on the appropriate colorswatch yourself). There is a seperate swatch for outline and for fill. Change it's color and all items with that color are changed. Now that I look at it again I see I uploaded the wrong file. I'd go for something like RGB 32 255 64 (the sideart green has a greater blue component than red, the green on the CPO does not). I used this reddish color to get something the correct color from my printer. Must have forgotten to restore the color before uploading. Actually the purple was a bit too light too (I suggest using 128, 112, 220). Will try to correct that on the library.
The Kickplate I did was based on the same colors I used in the sideart. The colors used in the CPO, are different and those in the marquee are different as well. Looking at pictures of cabinets these colors would be different on actual cabs too. So, the pieces of artwork do not seem to be colormatched on a real cabinet (well the kickplate and sideart are, but the rest isn't).
Here are two images that will hopefully explain better what I tried in words:

Picture of the original sideart. BTW this picture is not very good so don't use the colors off this, but it shows the difference between dark and light green very well.

picture of a Galaxian cabinet converted (or as the seller claimed, restored) to Galaga. The latter shows only one green color (if you look real hard you can see the slightly darker green though) and you can clearly see the green on the CPO is way different from the sideart. And then again the marqee has different colors again. Allthough the marquee green seems to look like the sideart green.