How do I convince my boss that too many link colors are bad for accessibility?

I work at a really small company making websites for a specific clientele, an older female audience.

My boss, also the lead Art Director, uses lots of different colors for links across an entire site. She's convinced that it makes information easier to parse, but not only is it really time consuming and obnoxious to write CSS for, it just looks bad. There will be 5 different link colors, all for the same link, with different hover states.

I'd like to explain how confusing and nonsensical this is with some usability articles, or use cases. We don't have any A/B testing cases or studies with this so I don't have any data to show her.

Anyone have any tried and true articles or design studies / post mortems, that they can recommend? Much obliged!