I definitely don't want Chromas sold only in packs; I am highly unlikely to want more than one Chroma per skin, similar to how I am unlikely to want more than one skin per champion.
I think Riot should allow players to "create" their own Chromas by making a tool that allows players to select colors for set parts of a champion (ex: primary, secondary, tertiary— any combination of three colors for three subsections of a skin/champion's model). If Riot is worried that some custom Chromas might be overbearing (ex: neon pink everything, everywhere, every game), they could simply not allow colors that are too bright (whether by limiting the editing tool or by manually approving custom Chromas).
The current pricing model I'm seeing for Chromas is overpriced (we'd effectively be forced to buy 3 discounted Chromas in order to get the one we want).
The proposed system also inefficient— Rioters are making these things individually, which takes time away from producing other content, plus they might not make the color combinations that players really want for each skin/champion.
I'm not sure how Riot could tie in Chromas to Champion Mastery without creating a connection that most players or Riot wouldn't find very appealing (ex: mastering a champion unlocks one specific non-custom Chroma for that champion's classic skin— any player that uses real skins would never use that Chroma, therefore, any player that uses real skins wouldn't care about that aspect of Champion Mastery). Another example: Riot wouldn't want to give one special non-custom Chroma for each of a champion's skins that would be unlocked upon reaching maximum Champion Mastery for that champion because that would probably be "too much work" for no real payoff. That, and any Chroma unlocked for free might not be as appealing as one you could purchase...
TL;DR: Riot, can you find a way to allow players to create their own Chromas? They're better at choosing the colors they want than you are. Just saying.
Also, please don't force us to buy bundles for the one Chroma we want.