Even though I concur with Tom's suggestion, it isn't hard to mix paint unless you are colorblind.
I do it all the time for model railroading and other touch-ups when necessary. The only problem comes if you want a quantity of paint, because the way I do it for touch-ups it's an inexact science of starting with a few drops of a base color that's close, then adding white to lighten or black to darken it drop by drop in the most simple mixing jobs.
I guess you
could count drops and record the results...
Any mixing when an exact match is important is done in a small empty jar that can be resealed like a head cement jar or Testors paint jar. When I think I am close to the color I am after, I put some on something similar to what I am touching up to dry overnight and seal the jar. The next day I compare the test sample to what I am trying to match
in bright sunlight and make any corrections to the paint in the jar if necessary.
If I were you, I would get some
Testors gloss model paint in the green shades and white & black and some toothpicks and start experimenting. The Penn "Greenie" color looks to be basic green, with less yellow so the Testors greens would be a good starting point with only lightening or darkening required, keeping in mind green can also be darkened with blue paint.
If you are totally obsessed and have the nerve, you can level any touch-ups like car fanatics do applying enough touch-up paint to create a raised surface when dry, then you
carefully shave that raised surface down with a razor blade and then sand it level with 1500 - 3000 grit sandpaper followed by polish & wax. I've done it on a car many, many times but never on a reel. However, I don't see why the process wouldn't work on reel with as much paint on it as a Penn Greenie.
As far as Sharpies go, you won't even come close to that color in a regular marker unless you look for
Chartpak AD Markers in an art supply store or online. However, I will warn you that permanent markers ain't so permanent, especially on non-porous surfaces. I know because Chartpak markers were all the rage eons ago for touching up the color of flies for an exact match to the natural. I bought into the idea 100% until I discovered my fingertips were becoming a distinct light olive color and my flies faded if I dipped them in a solvent-based floatant.
Bottom line if you go the marker route, expect the dye to come off on sweaty hands or if you get anything other than water on the reel.
Good luck!!