Gradient fill + uniform noise
Gradient fill is easy to make and used very often -- especially the linear gradient. In Paint Shop Pro 4 it is very easy to make:
Now, to make the fill, click somewhere in a new truecolor image with the Flood Fill tool.
You will notice that some sharp edges, which are not very nice. These edges are less visible with high contrast colors. The edges can however be removed by using the Uniform Noise filter. Select: Image, Special Filters, Add Noise, Uniform. You should use about 2-4% depending on the contrast of the colors. Use the Preview to see what is nicest.
Linear gradient, low contrast colors
Above with 3% uniform noise
Linear gradient, high contrast colors
Above with 2% uniform noise
Paint Shop Pro can make three other kinds of gradient fill.