ASC Files as a layer

I am recently working with Cartographica and producing maps with several layers of information and now I would like to introduce an .asc file with the total harvested area of rice, however, it comes formatted in a way that when I open that specific layer in Cartographica I can only change the opacity, since the color is automatically defined as a visible spectrum gradient.

-Is it possible to change the colors of this gradient? For example, use a gradient of green?

Furthermore, when in Cartographica I do "Show legend", it only shows me the legend of the layers used.

-Is it possible to make it show also the legend of this .asc file gradient?

Many thanks in advance for all input.

Nidia