Degradado de rellenoen Fresco '

I don't think you can make a gradient or mixed colour for the fill tool.
You can make them for the Pixel, Oil and Water Colour brushes though.
To create a mixed colour brush, paint the colours you want next to each other, then use the eyedropper to sample the colour combination into a single brush.

Hope this is what you meant, I used Translate to be able to read what you had written.