Font colour of footnotes

I have about 100 footnotes in my manuscript. When I compile the manuscript as ePub, most of the footnote numbers appear in blue. But some appear in black. I am referring to the footnote number that appears at the anchor point, not in the endnote list. See attached example, where footnote number 96 appears in black.

How can I control the colour of the footnote numbers? I want them all to be blue. Thx

I did some further testing and found a potential clue. When I insert footnotes into my manuscript (using Format > Footnote), the footnote anchor point sometimes is marked with an outlined box (footnotes 1 thru 5), other times with a solid box (footnotes 6 thru 10). I have not been able to determine why there are two different anchor types. See image below.

When I compile to ePub, however, I see that the outline box markers produce black footnote numbers, and the solid box markers produce blue footnote numbers. So there seems to be a link between footnote anchor types and the resulting footnote number colour. Anyone have thoughts on this? Thx