Knight of New Alara

Each other multicolored creature you control gets +1/+1 for each of its colors.

Fallaji Wayfarer

Fallaji Wayfarer is all colors. This ability doesn't affect its color identity. (It can be in any deck whose commander's color identity includes green.)
Multicolored spells you cast have convoke. (Your creatures can help cast those spells. Each creature you tap while casting a multicolored spell pays for {1} or one mana of a color that creature is.)

Demand

Search your library for a multicolored card, reveal it, put it into your hand, then shuffle.

Supply

Create X 1/1 green Saproling creature tokens.

Supply // Demand

Tome of the Guildpact

Whenever you cast a multicolored spell, draw a card.
{T}: Add one mana of any color.

Guildmages' Forum

{T}: Add {C}.
{1}, {T}: Add one mana of any color. If that mana is spent on a multicolored creature spell, that creature enters with an additional +1/+1 counter on it.

Dragon Arch

{2}, {T}: You may put a multicolored creature card from your hand onto the battlefield.

Glass of the Guildpact

Multicolored creatures you control get +1/+1.

Vivid Revival

Return up to three target multicolored cards from your graveyard to your hand. Exile Vivid Revival.

Reborn Hope

Return target multicolored card from your graveyard to your hand.

Rienne, Angel of Rebirth

Flying
Other multicolored creatures you control get +1/+0.
Whenever another multicolored creature you control dies, return it to its owner's hand at the beginning of the next end step.

Jared Carthalion

+1: Create a 3/3 Kavu creature token with trample that's all colors.
−3: Choose up to two target creatures. For each of them, put a number of +1/+1 counters on it equal to the number of colors it is.
−6: Return target multicolored card from your graveyard to your hand. If that card was all colors, draw a card and create two Treasure tokens.
Jared Carthalion can be your commander.

Vanishing Verse

Pillar of the Paruns

{T}: Add one mana of any color. Spend this mana only to cast a multicolored spell.

Obscura Charm

Choose one —
• Return target multicolored permanent card with mana value 3 or less from your graveyard to the battlefield tapped.
• Counter target instant or sorcery spell.
• Destroy target creature or planeswalker with mana value 3 or less.

Urza's Filter

Multicolored spells cost {2} less to cast.

Obsidian Obelisk

Obsidian Obelisk enters tapped.
{T}: Add {C}.
{T}: Add one mana of any color. Spend this mana only to cast a multicolored spell.

General Ferrous Rokiric

Hexproof from monocolored
Whenever you cast a multicolored spell, create a 4/4 red and white Golem artifact creature token.