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Personally, I think green should be a dominant color - it's got mana production and land search enough for all the other colors. Dual lands are a good idea...
Don't forget - Artifacts are cards, too.

Basing a deck on mostly green sounds good in theory. But in reality it really doesn't work to your advantage. Oddly enough I found spells that tap one of your creatures in exchange for mana to work the best in the long run. Artifacts that allowed you to produce different types of mana work good as well if used in moderation. You shouldn't go very far past ten percent of your deck in mana producing cards as a rule of thumb not counting the artifacts. Cards that allow you to draw other cards will help out greatly in a multi color deck. Just make sure your main base is Blue not green.

Another way you can go about this is black as your main base. Sacrificing creatures to gain mana to gain an edge. You can use artifacts to transmute the black mana into other types for use. I often find myself taking my deck apart and putting it back together sometimes completely untouched. I don't always use the knowledge I have and often like to play a more balanced deck than effective one. I played all of the colors and choose them in this order. White/Blue/Black/Red/Green anyway that is all just from my experience.