User blog comment:American che/The Genetics Behind Phineas and Ferb (actually quite interesting)/@comment-1647442-20100508032100

I completely covered this last year, and its very difficult to figure it out until we know what Clyde's hair color was when he was young. I believe it was brown, so that means, since Clyde is Linda's father, Candace does have a brown haired gene, which completely solves it.