label changes it color automaticly

i have designed my game with NGUI, and i have some uilabels in that, for some conditions their color is black and for other their color is w$$anonymous$$te. i have attached box collider to it and uibutton script to it as well. it changes color where ever i want. but sometime the color of label is black and mouse cursor is on that label it automatically changes the color to w$$anonymous$$te. so there is no code i wrote on mouse over or somet$$anonymous$$ng so how can t$$anonymous$$s possible? is there anyt$$anonymous$$ng regarding tween alpha?

please help