How to set the background colour for image in ssrs?

Hi All,
I have a gif image with conditional visibility in my ssrs report, which i kept in seperate textbox which takes the size of image.
I have to set the  background colour for this image.
Can anybody tell how can i set the background colour of the image in ssrs report?
Also one question.?when i put this image in rectangle it doesn't get exported excel?

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Bhushan