Golden Gimmick is the first level of Rainy Vista. It introduces a new key type, the Master Key.
Tired of the same old key colors? Try the Master Key! If you have a Master key, you can press [X] to use it instead of a normal key. They will open any door, no matter the color or size! If you change your mind about using one, just press [X] again. (Also, yes, calling them gold keys is fine too.)
(Note: The [X] part matches your Action control, and thus may be different if you rebind your keys.)
The master keys can be used to open doors you don't have the proper keys for, as well as help conserve keys you would have otherwise spent.
Because there is a purple door with no purple key, a master key must be used on the purple door.
On the right side, the two master keys must be used on the double doors to conserve enough white keys to get to the goal.
Pick up the master key.
Press [X] to use the master key to open the white door.
Pick up the master key and white key.
Open the white door, then press [X] to use the master key to open the purple door.
Pick up the master key.
Use the master key to open the upper white 2-door, then pick up the 2 white keys.
Open the upper-right white door and pick up the master key.
Use the master key to open the lower white 2-door, then open the final white door and touch the goal.