The Color of Magic

[diamondedge83]

The Color of Magic? GNU Terry Pratchett


The color most likely has to do with what element the energy source aligns with. Ceruleum being blue could mean it's water/ice aligned, though it is flammable and volotile. That being said, in the Eighth Umbral Calamity, Black Rose rendered Ceruleum inert, and Black Rose, despite it's name is Light aligned (because it causes instant stagnation of Aether). It could be that Ceruleum is Darkness aligned though that's always been like a dark purple. Perhaps black rose just stagnates all aether. Or like you said, it could just be personal preference because it looks cool? From what we're shown it looks like all the purple tech in Dawntrail is lightning aligned.

[kaynide]

Yeah, I couldn’t help the Prachett reference

Color seems kinda wild, because if we go by the crafting crystals and/or elemental sprites, we get:

Red=fire
Yellow=earth
Blue=water
Green=wind
Purple=lightning, but it’s a bright neon purple
Cyan=ice
White=light
Black=dark, but dark purples are also used

This color scheme carries over from FFXI.

I thought about Japan’s culture a little, and I am inclined to think the blue of the Crystal tower, the aetherytes and even Hydalaen aren’t necessarily water, but rather pure (maybe balanced?) aether. If we look at classic FFs, that light blue seems to be the default “Crystal” color.

Why? Well…
This is of note, perhaps… in English, blue is quite a “big” word, and light blue or navy blue or whatnot are considered to be a “blue”. In Japanese, light blue (mizuiro, which oddly means “water color”) is considered its own color, independent from blue (think like pink and red).

So, I’m inclined to believe:

Blue (as in royal blue) = water (like found in the pixie dungeon)
Cyan = ice
Light Blue = pure aether?

This makes me think that the Allagan machines used “pure-ish” or as pure as we can get, rather than, say, ice aether.

…but like Cleretic said it could just be aesthetics.