I have conquered the slippers!
Using some of the brown sections of yarn from the other colorway I had, I was able to finish the slippers. As Marilyn suggested, I ripped out the existing foot and used that yarn for the flaps on the second slipper, so that the flaps on both slippers would be blue. Then I reknit both feet using the new yarn.
I think they came out pretty well. I even managed to make the feet somewhat matchy.
Pattern: Allegria (Drops 158-48), not yet in Ravelry database
Yarn: Drops Big Delight, colorway “Marina” for leg, “Summer Meadow” for feet
Needles: US6/4.25 mm
Other than the issue of running out of yarn (the pattern has now been updated to the correct amount of 200 grams), these were a pretty fun project. The construction is very different, which is one of the reasons I wanted to make them. But since there was no schematic in the pattern, and the English translation of the Norwegian pattern left me a bit confused, I really didn’t understand quite how they went together when I started. But once I got going with the knitting, I figured it out.
I put extensive notes (including my own crappily-drawn schematic) in my Ravelry Project.