My sourdough starter has turned yellow is it still good?

Sounds like your starter has dried. Keep the starter in a cool place (fridge is too cold). Feed it every few days with flour and some water. Before adding the flour and water, discard maybe even half of the starter (best option is to bake every few days). Otherwise you'll end up with several pounds of starter... As with all food, use your senses. If it tastes and smells OK (for sourdough starter...), it's OK. So, to save your yellow starter, add a little moisture and fresh flour and see what happens. It takes a few days for the right growth and bubbles to appear.

To be on the safe side make a new starter.Quick and easy with 1 cup flour, 1 cup milk kefir. Mix thourougly, let stay in room temperature for 2 to 3 days till it's bubbly. I always use the whole amount of starter -sometimes 500g- in my bread. Don't forget to keep some aside for the next bread. Kept in the fridge you only need to feed it every 7 to 10 days. Before the next baking feed your starter every 12 hours till it's bubbly.