I'm relatively confident it's based on crafting skill or completely random. I'd think it's the first one but don't quote me on it.
It took me a while to realize those white modification recipes can yield higher quality items too. It's arguably a bit annoying because it leads to unnecessary crafting. Instead of making a couple mods to slap on an item you end up making 20 until you get good versions.
As noted by Valethaar the perks apply to recipes of a specific tier. So to make an epic you need an epic crafting perk. This doesn't appear to apply to those white generic items. It's another example of a mechanic where better clarification is in order (hint hint, updates can probably fit that in there without a ton of work).
I'd add, that little tidbit where a white mod recipe can yield much higher tier items is kind of important. If you didn't know this crafting might seem lackluster. It's really not though, as a mod for armor or something can offer more protection than the armor itself. In fact, it would appear it routinely does as you get to higher level gear. A single armadillo mod can yield like 250 armor, for instance. Even many lvl 50 items don't have 250 base armor.
Without trying to wall of text your simple question, you can use the behavior of those mod recipes to kind of cheat on getting crafting mats too. You can spend white/green mats to make a purple, disassemble it and get higher tier mats. It's not very efficient on mats or time but it's an option.