I did create, but in level blueprint, so I moved it to MyCharacter BP. Now the casting is fine 
Tell me one more thing, please. In the picture you can see my interface - these are buttons created in other blueprint. Now I just need to get the values which I set manually (SmallIntColor and SmallIntSlot). When I try to do that I get the default zero values because they are zeros in blueprint with single button. Do I need function in ColorInterface with casting to InterfaceSlot or what?
Great thanks for help so far!
