Thinking about a mana base for a legacy {cromat} deck any ideas ? I love this card
Firetly I don't know much about legacy, but for a mana base personally I'd start with some good multi colored lands, even some of the shards of alara set ones with 3 colours. {crumbling necropolis}, {Jungle Shrine}, etc.
Also look at the 3 colored mana tapping artifacts as they will be easy to buy and then give you colours you need .{Obelisk of Bant}, {Obelisk of Grixis}, etc
Next up look at things like {manalith}, {Rupture Spire} that tap for any colour, or {chromatic lantern} to change colours of whatever lands you do have. After that I'd say you are pretty set to run whatever. Also run plenty of draws if you can, and maybe even stuff that let's you play more than one land per turn.
Also you might like to run cards like {Obelisk of Alara} and {Door to Nothingness} in your multicolored deck :)