Customisation doesnt change

Hi there!

I am building a new website for a client, but am having trouble making changes in the customisation. I need the whole background of the home page to be yellow, I do change it under customisation, it changes in the preview, I have definitely saved it, but it keeps reverting back to the old settings.

Enclosed is a screen shot of what I need, will send another message with private log in.

Thank you!!!
Sarah