The Tuscan city of Lucca has many a quaintly unkempt building and this one fits nicely into the challenge to find something mustard. I hope you like.
My second take on 'mustard' is the Chama, NM, ticket office for the narrow gauge Cumbres and Toltec railroad. This is such a super day out even if you think trains are not your 'thing'.
I hope these cut the mustard 🙂