Something very funny is happening with Calibre: I've put both (a & a:link) codes into the CSS field & trhe first book came out with the color I wanted.
Then I tried a second book with the same (copy & paste) code & it reverted to blue.
I then tried the first book again & it also came out blue.
So far i've tried a few additional books but
no repeat performance from Calibre - TOC remains blue.
A mystery!