Make line number colors match bat for the same theme?

In trying out delta I noticed that the line number style delta uses doesn't match what `bat` uses for the same theme. Here's a screenshot:


The line numbers are hard to read in delta but not in bat. It looks like the line number style can be adjusted in delta, but it would be nice if it would naturally follow the theme, as in bat.

Reproduce the screenshot using the same theme in delta and bat, then trace how each tool determines line-number colors. Done means delta line numbers are as readable and theme-consistent as bat's for the same theme, without requiring manual adjustment.

Written by the indexing model from the issue text.