Chromatic Lantern

Lands you control have "{T}: Add one mana of any color."
{T}: Add one mana of any color.

Sol Ring

Swamp

Mountain

Command Tower

{T}: Add one mana of any color in your commander's color identity.

Plains

Reliquary Tower

You have no maximum hand size.
{T}: Add {C}.

Island

Forest

Exotic Orchard

{T}: Add one mana of any color that a land an opponent controls could produce.

Fellwar Stone

Tome of the Guildpact

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

Chromatic Orrery

You may spend mana as though it were mana of any color.
{T}: Add {C}{C}{C}{C}{C}.
{5}, {T}: Draw a card for each color among permanents you control.

Omnath, Locus of All

If you would lose unspent mana, that mana becomes black instead.
At the beginning of your first main phase, look at the top card of your library. You may reveal that card if it has three or more colored mana symbols in its mana cost. If you do, add three mana in any combination of its colors and put it into your hand. If you don't reveal it, put it into your hand.

Arcane Signet

Cascading Cataracts

Indestructible
{T}: Add {C}.
{5}, {T}: Add five mana in any combination of colors.