Hi,
I just looked up some relatives and that page includes mostly black ink, but additions in green ink, red, a pale blue, and regular blue ink. The pale blue looks unusual - and your pink ink would be too.
My guess would be that the inks may have faded or changed over time? They added details such as married names at various dates, so different pens would be around.
Maybe they wanted those later additions to stand out, with colours used.