When converting from Excel, the sparklines are changing to have a black background. How do I prevent it?

I am converting a spreadsheet from Excel.  It contains sparklines from other tabs in the file.  when I do the conversion, the background of the sparklines is changing to black making it difficult to see the lines.  I have changed the color of the sparkline to a lighter color which helps to be able to read it, but it does not look good with the black background.  How do I change it so there is no background?  Thanks.