You should have no problem custom mixing the blue & white like you did for your MFG, as long as the epoxy paints are the same line by the maker. Accurately measuring the volume, repeatedly, might be a little tricky as many epoxy paints tend to be a tad thicker then oil based paints, IMO.
But given how the MFG turned out, the work you've done on the SIL project boat, and what you've done on Charles Ouachita, you should have NO problems getting to the shade of light blue you want, epoxy paint & all.
If Vinyl Approach can't get you the logo in the color, style & size you want, try GarzonStudios. I'm extremely pleased w/ the work they did on my SeaNymph capacity plate. Changed the standard font, changed the style of the plate, and changed the 'parent' company listed on the plate.
From a bad pix of my original:
To the new one:
It only took 2 emails back & forth from sending the request to final approval of the proof. New sticker arrived 6 or 7days after my initial email. Great outfit & couldn't have been easier to work with.