I have a fruit still life with lots of layers making up the elements of an onion, tomato etc. They are all sitting on a white background on the canvas layer. I would like to put in a coloured background behind the fruit.I have tried filling the canvas with the colour, and putting in a new layer above the canvas and filling that with a colour, but in both cases, it interacts with the colours of the fruit above, whatever blending modes I try in the new layer. The fruit layers on in gel blending mode, and I have not tried changing all of those. How can I achieve my objective?