A fungal nail infection generally starts out as a slight yellowish tinge to the nail, or even a white spot. But as the fungus begins to spread and mature, it can turn a yellow, green or even black colour. Because the nail is designed to be strong, removing an infection from the nail bed can be tricky.
Drying thoroughly between your toes after a bath or shower is a god idea. It's also worth keeping your nails trimmed - cut straight across, not going too close to the skin. Shoes that allow your feet to breathe and your toes to wiggle prevent the conditions that fungus thrives in. Please consult a Heath Care Professional for advice.