a white report has to be filed with the california department of real estate in order to go to sign a contract, put money and escrow and close.
a yellow is one step below and is not always filed by the developer, typically it's only filed when the developer is in a rush to get buyers under contract while they are trying to fufill some conditions outstanding on their white (i.e. filing subdivision), i think at this point, having a yellow allows the developer to back out still, but not the buyer, however, it's still very easy for the buyer to back out because if there is any miniscule change in the interim between the white and yellow, the buyer can claim they didn't know what they were getting into and back out.
Pink is just to get a sales center open and start advertising, they can only take a deposit check that is fully refundable at the buyer's request.
I've done a little work on this stuff and it's extremely tedious and confusing.