The word orange came from the tree the fruit grew on, not the fruit or the colour. Before that an orange called the 'fruit from orange tree' which just got shortened down to orange. Before that the colour orange was called yellowred.
So the reason why an orange is called and orange is because it was the colour that was named after the fruit, whereas yellow and lemon weren't associated with each other in that way. Also lemons start out as green not yellow ☺️
