The third one isn't live yet, but like the first two I have a proof copy, and like the proof copies for the first two it is too dark.

The covers have to be submitted to Kindle Direct Publishing in CMYK, and I make sure to set to CMYK in PagePlus when creating the cover file to submit.

I asked about this issue on the KDP forum, and learned about gamut. Apparently the colors I have chosen were out of gamut for print.

If I understand correctly, there's no science for choosing the in-gamut print color which appears closest to an out-of-gamut screen color, which is why the software chooses something unsatisfying. Apparently only our eyeballs can make a satisfactory choice.

After reading about this and watching some Youtube videos, I understand that Adobe helps with this by giving you a color picker for print that only offers in-gamut colors. So you can eyeball what looks closest to the out-of-gamut color.

Is there anything PagePlus can do to help me choose the right color?

BTW I'm using PagePlus X9. Some of the Kindle covers were created in earlier versions but I'm using X9 for the paperbacks.

Here's an example of the difference. It's a children's book about foxes, and I found a color on the web that was said to be the color of fox fur. That worked fine for the Kindle edition, but the KDP paperback is brown: