I think I know a *possible* workaround (not really).
I've been TESTING around....
I made a NEW GAME *default world state*. And right after cassandra and my inquisitor opened that first gate out of haven, while running up that pathway before the bridge collapse, the boots turned tan. Right after falling down the bridge collapse, it went back to normal mercenary boots colour (dark/black). It didnt change since then. Even when solas used the inquisitor's hand to close the rift for the first time.
I tested this "default world state method" 2 times with rogue/warrior with the same positive result. Its as if it happens less with the default world state character.
Now, I started a new game using a custom world state, or other people's save files (from nexus for example), i tested this. Running up that same path, the pants turn tan throughout the whole mission and never faded back to normal color.
Basically I have a theory its related to custom world states somehow (as far as the duration of this dust effect).
Can anyone else test this?