Most of the beaches in Iceland are pitch black, some are rocky and wild, some do have soft black sand while others are covered with white/yellow sand. The white beaches are rare though but for example in the Westfjords you can find some white or yellow beaches and also at Snæfellsnes peninsula in west Iceland.
If you are driving around Snæfellsnes then I recommend a stop at Búðir. There is something very special about this place and this area even though there is absolutely nothing there except one hotel and a church surrounded by endless lava field, "Búðahraun" and some beautiful windswept grass.
Búðir is a former fishing village but as so many settlement in this area it was abandoned in the early nineteenth century and today consists of nothing more than the hotel and the beautiful black little church that are situated just a short while from the sea with its yellow sandy beach and some rough lava rock formations too. If you go to the beach sometimes if you are lucky you can even see some cute and curious seals
Many wide travelled people have stated that nowhere in Iceland have they enjoyed the natural surroundings more with the nearness of the mysterious Snæfellsjökull glacier and it is really true there is some special energy around there.
In summertime I recommend doing a little picnic in this area. Its so beautiful and cozy sitting on the beach or just find some nature made seat from lava rocks, relax and just be and enjoy. You will not be disappointed and after a while you are full of positive energy and happiness. If you love photography then this area with the black little church in your frame is very picturesque, also in winter time. Maybe you don´t want to do a winter picnic but still its worth a stop and a walk down to the beach.