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.