Everything goes. I wear black tights and brown leather shoes, dark tan shoes, they all look fine. Of course some things will go better with others but there is absolutely no reason why a pair of tan boots wont go with black leggings. If you have thick set legs you may find that tan boots break up the look of the leg and make you look stubbier than if you had just black ones. They would give you a longer leg. It also depends upon the length of the boot. Calf length ones look fine but knee highs depending upon where they stop can shorten the leg. Its just a case of experimenting in the mirror.
I am currently wearing socks with my leggings cause they are in my boots!! You dont see them and unless i want that look i just tend to wear ones that dont come up so you see them. I had biker boots [black] and navy leggings on today. They looked fine!!