I've had a tube of Indian Yellow (green) hanging around and today I tried mixing it with some Burnt Umber. It produced the most beautiful muted olive/gold/yellowy colour, fantastic for foliage or grass.
Various manufacturers will call it something different, but it will be called something like Green Gold or if you're into pigments, look for something with PY129. Well worth a try for landscapes.
Anyone else have any good colour mixes to share?