This is the only one with a drawback for having the third color, which really sucks

@dude1818 I didn't mean for this effect to be a downside. But now that you mention it, I can see how you can see it as one.

TBH this might be balanced enough to say "gets +1/+1 and gains First Strike if you control a black permanent"

I mean, 2 mana 3/3 first strike is a bit good, but getting it on turn 3 isn't as big of a deal as on turn 2. to get this on turn 2 you'd need realllly good mana fix. I mean, like, swamp and red/white shockland in that order, or something which can get you any colored mana in significant amounts. If you don't have that in your format, than making this a (possibly) 3/3 first striker for is pretty balanced. Even in vintage with it's insane mana rocks, lotuses and straight up OG dual lands, this idea wouldn't be that powerful, because you can easily get out something way stronger, even sooner.

The main issue with this getting a -1 toughness is that it becomes the weakest it can be. Literally 1 damage will kill it. there is no 0 damage in the game. If this started as a 2/3 and became a 3/2, it would be less weak, but also still wouldn't be very decent power-wise.

Perhaps you have a mechanic or theme in this set that synergizes with a 3/1 (such as caring about high power or low toughness), but if not, you could probably just give this +1/+1 and first strike, or if you feel that's too strong, +1/+0 and first strike could also do.

Keep in mind, is more than capable of having first strike, but + only share (1) keyword (from what I know): which is first strike (black barely gets any). The flavor isn't ideal, but I don't know the flavor of this card TBH either.

It's a neat cycle, but it's both poorly and well designed. It's well designed because it can heavily encourage any tri-color archetypes, but overall the effects are rather weak (you've fixed most the cards though, so grats on that).

All in all, pretty good card idea, but this needs to be tweaked. On creatures, a 2/2 creature is normally way better than a 3/1, unless it has Haste or another aggressive-ability (perhaps Trample) (which aren't in colors, unfortunately.

EDIT: Alternatively, you could keep the +1/-1 and grant first strike, that would be better (though remember, it would still die to any non-combat damage, since first strike is only for attacking/blocking)

nice idea @Froggychum, thanks for the detailed criticism!