JennyEmma is close. But on the 2nd time I played the puzzle, I picked the intial number 18, which was violet in color. The next frame is obviously there just as a distraction as is the third frame. When asked to pick the correct house, the number 18 displayed in it was actually orange in color. But that didn't matter either as we are working with simple matrices. When I chose the color of the number, there were three collumns with a violet number in them. When I picked the house, each house had one of the initially violet numbers in them. By picking the house with the correct number, a simple compare statment was used to match the collumn with the only violet number in it and voila, you have the number eighteen. The door chosen didn't matter. Any door picked would have given you the same answer.
You have to remember, this is a software sorting routine that works by simple comparison, or if-then, goto statements. Each entry you make flags the program to enable a subroutine that narrows the field. And with such a limited field, it takes only three of four entries to solve the puzzle.
Hope that was crystal clear.
Seeeeeya; Goodweed of the North