Background colour change problem

hi all

i have some code that once i hit a button it will change my background mc colour to the chosen colour, now the problem i have is that my backround mc that i apply the different colours to starts with a gradient fill, now when i apply the new colour to it the grident is lost and i just got a solid colour, how can i get it to keep the gradients when changing to different colours.

hope i make sense thanks in advance