Sum of Colored Cells

Hi,

I'm trying to auto-sum some numbers in excel. On the spreadsheet I attached, I need to auto-sum the numbers in last month's column (in this case, feb). I need to generate two sums, one for all the white cells in Feb and one for all the red cells in Feb. Keeping in mind that I will be adding new months every month and that the formula needs to keep up, I was thinking of having it find the total column and then go to the previous column, since that will always be last month, then add all the white cells and all the red cells, but I have no clue how to do this or if there's a better way. Does anyone have any advice?

Thanks!