read the Codex, it has a lot of information. much of the Codex was updated recently.
Set Affixes (Green) can have their Rank improved by…
multiple items with the same Set. 6 Items with Equality Set will be Equality (6).
+All Sets. either Items with the Legend All Set (can’t be rolled with Ruby) or the Myth Stone with All Set, or a combination of both. the max for these is +4.
with Set Affixes on Items and +All Sets, the max is Set Affix (8). 4 Items with Equality and +4 All Sets will give Equality (8).
Normal (Yellow) and Epic (Orange) affixes can be rolled with Angelite.
Epic (Orange) affixes can also be rolled with Topaz.
most Legend (Red) affixes can be rolled with Ruby. the rest can only be found on looted Items.
many Set (Green) affixes can be rolled with Amethyst. some can only be rolled on certain Classes, and the rest can only be found on looted Items.
Crystal (Cyan) affixes can be rolled with Obsidian. Legend/Eternal Items have a chance to be found with Crystal affixes.
Mythic (Purple) affixes can be placed on Items by placing a recipe of 4 Myth Stones on Items with Sockets.
not sure how updated this is, but the Wiki has a lot of helpful info.
this should help you with many of your Crystal questions.
this is an old Post, but it has lot’s of helpful info for new players.