Open Illustrator PDF on Photoshop, colors washed out

Hi there! Whenever I export a PDF including dark-grey lined table chart from Illustrator, it seems well and is printed out well.

But if I try to export it as JPG or PNG the color washed out and looks extremely light. (I've changed color mode into RGB before saving)

And when I open the PDF in Photoshop it looks extremely light grey, too.

Am I doing something wrong? Thanks in advance for your time!