I have observed the requirements shared and have worked with the presentation file on my end. Actually, the issue is not related to Aspose.Slides. The template chart is using Automatic fill color and fill type which is not recognized by Aspose.Slides. I have also created an issue with ID SLIDESJAVA-34330 in our issue tracking system to further investigate and resolve the issue that why automatic fill colors for chart series are not read.
In the mean while, I suggest you to please set the solid fill type for chart series collection and their respective colors. Then when you try to access the color and fill types, you will get the right values. I have also attached the modified presentation and suggest you to please try accessing chart on slide 2.