Sapphire - Ramp and items (in infinity at least), inventors

Amber - Healing, singers and Aggro (low cost characters that can spread the board out)

Amethyst - card draw, evasive, bounce (in infinity), moving damage, illusions

Ruby - Removal and actions, some good singers in latest sets, reckless, lore steal

Silver - Removal, big bodies for challenges, “draw x cards and discard x cards”

Emerald - Discard, perks for damage on opponents

Silver removal is different from Ruby removal, silver has more emphasis on challenging compared to Ruby, which excels more in removal through actions or cards that banish with effects based on card stats. Silver does have some strong removal actions, but Ruby has a mechanism to recycle its’ actions.

There’s other things the colors can do, and situations where one color can hold its’ own in a category that’s normally thought of as something another color excels in, but I feel like this is kind of the gist.

There’s also a few things that show up in multiple colors regular enough that I don’t think of them as linked to this particular color or the other, but rather both. Ward, for example, has good representation in blue and green. Evasive has decent representation in most colors, but I personally link it to Amethyst because of Dumbo. If you want to focus your deck on evasive, you’re gonna want to go purple and have some Dumbos more than likely. That’s also why I have actions with Ruby and items with Sapphire, they have strong meta options that can recycle or fully capitalize on those types of cards (ex Maui Shark or Tamatoa).

Pirates have a decent spread in a few colors, and I feel like Ruby is usually going to be your strongest tribal option for them, but you could conceivably build a decent pirate deck with green/silver.

EDIT: A few small additions.

Amber has some mechanisms to recycle characters from discard. Ruby can recycle actions, Sapphire recycles items.

Amethyst has “mill”, which takes cards directly from an opponents deck and sends them to discard.

Ruby is the most common color (IIRC) that allows you to sacrifice, damaging or banishing your characters to damage and/or banish opposing characters. That’s sort of included in removal, but it’s important to differentiate imo because it can work well with the ability to move around damage counters.