I still like white or off white background, black text and a little color which has kind of stood the test of centuries of use.

Here's a bit of the St Cuthbert Gospel from 1315 years ago https://wiganlanebooks.co.uk/wp-content/uploads/2013/10/st-c...

and somewhat similar in sublime text (Calydon light) https://packagecontrol.io/readmes/img/5621a2861cccff9b1d2d2b...