House Icons
The current House Icon colors are:

Cyan - For Sale By Bank
Red - Owned / Not For Sale
Green - Owned / Co-owner / Renting

House Purchasing
You should check out as many houses as possible before you purchase. There are over 800 houses in Los Santos/Senora Desert, each with a different price and style.

Houses can be sold by the bank if they are unoccupied, or they can be sold by the owner. The Bank typically sells houses for their current value. House Owners can also set their own sale price to sell to players. To start off, houses allow you to save 1 vehicle in the Garage. You can purchase additional Garage space when you stand in the Garage checkpoint.

House Ownership / Co-Owner / Renting
Each player can own 2 different houses, and co-own 8 different houses. Each player can also rent 10 different houses. Once you have purchased a house, it will remain yours until you sell it.

If you quit inside a house you have access to, you will respawn there when you rejoin the server. Park your car in the Garage before you quit in order to save it. 

House Co-Owners have complete access to the house and its storage, except for the house sale price. Co-Owners and Keyholders can quit and respawn at a house, and they can also use the house's Garage. Keyholders cannot access the storage and the garage. 

Houses are subject to property and/or co-owner taxes. Property and Co-Owner taxes are automatically paid every 2 gamedays. Failure to pay your property taxes will increase your tax debt. These taxes apply to all players, including donating players. Taxes also apply to your house storage.

House Owner / Co-Owner Menu
Once you're inside a house that you own or co-own, type /house or walk to the front door to access the House Menu. There are many options including:

Sell: Sell your house to the bank for the amount specified. 
Rename: Change the name of your house.
Inventory: Store a range of items in your house storage.
Upgrades: Purchase a Wardrobe for unlimited player outfit changes, a Drug Den so you can cook drugs in your property and Upgraded Locks to make it more difficult for players to break into your house. 
Change Locks: Removes access for all Co-Owners and Keyholders. 
Remove Co-Owners: Menu to remove specific co-owners from accessing your property.
View Keyholders: Menu to see who has keyholder access to your property. 
View Co-Owner: Menu to see who has Co-Ownder access to your property.
Kick Players: Kicks a specific player who is currently inside your house outdoors.
Order Home Delivery: Purchase food/items for your house.

House Robbery
When you successfully break into a house, you may rob the property. You can only rob a property if the owner or co-owners are online. Enter the red checkpoint to view the property menu and select "Rob this property" to steal from the property. You will receive a wanted level when you attempt to or start to rob the player's property. Search the property by walking around to find loot and stashes. Exit the property to complete the robbery and receive your stolen goods. 

House Visiting
Innocent civilians and Law Enforcement Officers can visit houses that are for sale to help them decide if they want to buy it. Once a house is owned, entry is limited to other civilians. Here are the different ways to enter an owned house:

Knock At The Door: If the owner is on the server, you can knock at the door. The owner can then decide if he/she wants to let you in. A door knock / answer will let you enter a house only once.
Break In: If the owner of the house is on the server, you can attempt to break in. If your break in is successful, you will be reported to the police.
House Keys: House keys give you access to a house whenever you want as long as the owner doesn't change the locks. You can carry up to 10 different house keys. If you already have 10 and receive more, the key that hasn't been used the longest is removed.

By default, house visitors without full access can place items into storage. They cannot remove items from storage, or see it's inventory however. This option can be set by the house owner or co-owner in the storage menu.

House Commands:
/house - Access the House Menu and House Information from inside a house
/houseinv (/storage) - Access the House Inventory
/housekeys - List the house keys you are holding
/housekick - Kicks a specific player out of the house
/housekickall - Kicks all players out of the house
/answer (/ans) - Answer a knock at your door and let the player enter your house
/cokeys (/setcoowner) - Give a player the co-owner keys to your house. The player will become Co-Owner of your house and have full access
/keylist (/keys) - Lists all the Co-Owner and Keys that you have