Because they need to ship it out with some sort of configuration. You can change it all you want later through the launcher program.
This is exactly the reason! I would recommend that you choose a color for the Diamond Pulse Mode, because none of the other pre-installed fonts will pulse, and this will let you see what the effect looks like. All the other pre-installed fonts have Aegean Silver (or white, to the uninitiated) as the Flash on Clash color, so feel free to choose something other than that for your FoC... but you might want to be sure it will contrast with both of the Pulse colors, or it might not be as much fun. Then again, you’ll be able to monkey around with that on your own later once you feel adventurous enough to use the Controller software, so... use your best guess.