Thank you for reaching out to us through the Community. To change the column width in a two column block, you will want to hover your cursor over that block. You will notice that there is a handle that divides the two columns. Click and drag the handle left or right to adjust the width of the columns in proportion to each other:
In regards to changing the color of the background of each column to different colors, that is not something that is possible at this time within Constant Contact. However, I have tracked this feature request to your account, notifying our developers about it. Let me know if you have any additional questions! Hope this information helps!
Thank you for reaching out to us! We have actually just recently released a layout in new 3GE templates that does allow for two different colored blocks to exist in a single row. If you select a new template from the "create" button in your campaigns tab, you will find a new sidebar layout.
For this layout, one color is controlled by the paint can in the little gear widget seen when mousing over the block and the other color is controlled by the "Feature Articles" color under the design tab!