If they are yellow on the inside they are sweet potatoes, if they are orange on the inside they are yams. Or vice versa. Basically, the color difference isn't an indication of ripeness, it's a different potato. However grocery stores interchange the name yam & sweet potato even tho they are 2 diff things.
Sweet pots/yams have a higher water content than potatoes so just watch your cooking time, etc. When you make the "fries" they may not ever get crunchy like regular french fries due to said water content. But I do make them as fries with olive oil & YUM! they are good. Baked with cinnamon, brown suger (sub splenda) and Molly McButter or other butter substitute is also yummy!