I am looking for a way to color a DB object with more than one color.

for example, a sphere with one half red, other half green and the colors smoothly blend together in the middle.

is there a way to use DB to do something like this? Without using fancy lighting, just colors

Create a 2d box (using the box command), which allows you to fill it with a gradient from one colour to another, grab the image (using 'get image') and use the image to texture the object, with the texture object command. Or, if you wanted more control over how it looks, you could create the texture in a paint program, and create the model in a 3d modeller and texture it there.

just use the vertexdata commands and change the vertex colors
simple