Just setting columns to auto height will do just that bcs the height if the columns wik be the height of it's content in this case the images, try adding a paragraph large to one of the columns you will see it displays the image and the paragraph the other one smdisokays just the image

Thanks for your replies. I'll keep trying.

You could give the columns some padding all around which would show the column background color around whatever content you place inside, you could add margins around the content too to give them some space between them.

It seems to me that the situation is as follows.

1. In Content > Elements > CSS Grid Based Layouts the Two Columns element was added to a page.

2. That element (Layout Class 'sd-two-cols') was given a background colour which showed on the SD canvas, but didn't show in Preview or 'Preview on'. The reason for that is that the height of the containers is set to 'auto', as Wayan correctly diagnosed.

A simple solution is to select the element (Layout Class 'sd-two-cols') in the Elements Inspector panel, and then to go to the Styles panel Layout section and Launch Grid Editor. In the Grid Editor change the height from 'auto' to a set height (such as in pixels or vertical heights, not %s) and click on OK in the bottom right hand corner of the Grid Editor.

Frank