When you acquire a mortgaged property through a trade or sale, you have two immediate options regarding the mortgage:

Owning a mortgaged property still counts toward completing a color group. You can still collect double rent on the unmortgaged properties in that set.

Before a player can sell or mortgage a property, they must first sell all houses and hotels in that color group back to the Bank at half price. Handling Bankruptcies

You must pay the Bank the mortgage value plus 10% interest. Once paid, the deed is flipped face-up, and you can begin collecting rent or building houses (provided you own the full color group).

If a player goes bankrupt to you and turns over mortgaged properties, the same "immediate 10%" rule applies. You must pay the 10% fee right away, then decide whether to pay off the principal or wait (incurring the extra 10% later).

You cannot build houses or hotels on any property in a color group if even one property in that group remains mortgaged.

You must still pay the 10% interest fee to the Bank immediately. If you choose to lift the mortgage later in the game, you will be required to pay the mortgage value plus another 10% interest to the Bank. Key Strategic Constraints