Wild tulips are always yellow. At least, they are in Martenastate, Cornjum just out of Leeuwarden. We joined a group for a tour on a spring morning that felt more like Siberia, where the wind most probably came from during our 1,5 hour tiptoe that could have been walked at a leiseurely pace in 10 minutes.
Our knowledgeable guide explained every seed and leaf. It was beautiful, we will cycle back in summer.