Is it possible to change the transparent place to white?

Hi,

I have a buttons in my UI Canvas, buttons have a transparent image .PNG format.
i want to add the white BG behind this button or along with this buttons. I already have a black panel, on the black panel my buttons appearing. When it appear i want to change the transparent to white.

Is it possible to add the image and set the layer value to adjust the image front and back position?

But i cant see any layer values in unity 5.3.5 version. Please suggest some good ideas to solve this...

Is it possible to change the transparent place to white?