Colored coins have already been implemented. ArmoryX is a color-aware Armory fork but it's abandoned because of Armory's resource consumption.
We currently have http://bitcoinx.github.io/webcoinx/ currently working on testnet, and there's a plan for a next gen client - https://github.com/bitcoinx/colored-coin-tools/wiki/The-next-gen-colored-coin-client.
More information is at https://bitcointalksearch.org/topic/chromawallet-colored-coins-issue-and-trade-private-currenciesstocksbonds-106373.
Colored coins are a layer on top of Bitcoin so it does not need to be "added to Bitcoin".
We currently have http://bitcoinx.github.io/webcoinx/ currently working on testnet, and there's a plan for a next gen client - https://github.com/bitcoinx/colored-coin-tools/wiki/The-next-gen-colored-coin-client.
More information is at https://bitcointalksearch.org/topic/chromawallet-colored-coins-issue-and-trade-private-currenciesstocksbonds-106373.
Colored coins are a layer on top of Bitcoin so it does not need to be "added to Bitcoin".
Just what are colored coins? 
The thing that is described here.How can you exactly "color" a bitcoin?
Thank you.
Basically, coloring is based on the ordering of inputs and outputs.
