Sidechains :
Sidechains are alternative blockchains which are backed by Bitcoins via Bitcoin contract just as dollars and pounds used to be backed by Gold. One can possibly have a thousands of sidechains “pegged” to Bitcoin, all with different characteristics and purposes--all of them taking advantage of scarcity and resilience guaranteed by the Bitcoin blockchain. The Bitcoin blockchain can in turn iterate to support additional features for the experimental sidechains--once they have been
tried and tested.
Colored Coins:
is an open source protocol that describes class of methods for developers to create digital assets on top of Bitcoin blockchain by using its functionalities beyond digital currency.
Alternative Blockchains:
Alternative Blockchain is a system of using the blockchain algorithm to achieve distributed consensus on a particular digital asset. They may share miners with a parent network such as Bitcoin’s--this is called merged mining. They have been suggested to implement applications such as DNS, SSL certification authority, file storage and voting.