Creating Gradient effect in Lotus Notes client is very easy. You just have to go to create a table in the form/page. Then in the Table Properties > in the Table/Cell Background tab you select Cell color. Then you select the type of style and choose the colors for the gradient. And your table cells are ready with the gradient effect.
However, this gradient effect is not visible in web. Thus, you have to find some other way to color the cells with gradient effect.