Changing colour and its gradients

I'm very new to paint shop so detailed responses would be appreciated. I have a simple image which is an area of colour with a white background. The edge of the coloured area blends into the background with gradient colours as if to make the edge of the coloured area appear smooth. If there some way I can change the main solid colour in the image and change the gradients so that they match the new colour. I have tried doing a colour fill but this only changes the main colour and not the gardients. help would be much appreciated.