I know it is almost impossible to judge gemstones by photos but I am going to indulge in a bit of guessing.
I think that the pink coloured stones in the earrings worn by the Queen in New Zealand (as in the photo posted by Cristina) might be pink coral. I doubt they are conch pearls as I suspect it would be almost impossible to find two evenly matched elongated pear shaped conch pearls.
In the earrings the Queen wore at the Australian War Memorial (as per Maridje's and Gert-Jan's photos) I wonder if the gemstones might not be mandarin garnets and yellow sapphires? To me the larger pear shaped drop looks a different colour from a deep golden brown citrine and the yellow stones also look different from a yellow toned citrine - but yellow sapphires do come in the colour range.
The pear shaped drops in the earrings shown in Maridje's superb photo of Princess Beatrix have a different setting (look at the number of claws in earch set of earrings) and I suspect are larger than those in Queen Maxima's earrings. To my eye the colour looks different also. I would be more inclined to think that the stones in Princess Beatrix's earrings are high quality citrines -- but of course it is all guess work as photos are not a reliable way of identifying gemstones.