Hi Martin,
Thanks for your sample.
We have checked the reported scenario in your shared sample, If the result of the search is beyond the limit count, then only the column is colored, which is the Kanban's default behaviour.
Initially in Inprogress column, there are 6 cards which means column count is greater then the constraint count so it is colored. After the quest, only one card (Count 1 of 6 Max 2) is shown on the kanban board so that the column is not colored.
Regards,
M.Vinitha devi