As you see in this image, the edge of the window is black, but I want to make it white, how can I do this in the besping settings?

Which edge are you referring to? The glow around the windows, the scrollbar, or the border? If it is the border, you will likely find this in the Window Decoration settings - particularly if this border disappears when the window is maximised.

I don't have activated the glow aroun the window, it was not the scrollbar, it was the border. I have achieved to shift the color by changing the corresponding configuration in Bespin's settings > KWin decoration hints > Active titlebar

Thank you so much for responding