Transparency map problem

[skubi]

Hello I have a problem. I made a cube and I want to have a sign on one side. So I made a material with orange color. I duplicate a diffuse layer and set second diffuse (duplicated diffuse layer) color to white. I made a bmp file (black backgroun and white letters). In first diffuse layer I click "M" right of the TRANSPARENCY and add bitmap (prepared bmp file). If I update preview, I see what I want: a orange sphare with white sign . But when I render it, the side of the cube is orange, but without a sign. Double sided is checked, if I uncheck, the side of the cube is not orange but black. Can someone help me please? Thanks