Something is happening with your test Sami, on my Photoshop, the grays are 102, 102, 102
on both images.
Probably the problem was when I saved them with "Save for Web" option after checked, just to make them less heavy.
On your test, you might had selected a random pixel slightly different than the others. An image, after repeated saves with different programs, can result corrupted. You've got completely another numbers for RGB... even for the second image, where they resulted be the same.
BTW, the stars ARE also the same blue:
(and size) (R51, G51, B102)
(Sorry for the grammar, I rewrote the above paragraph ten times without find the correct way...hope you understand)Are really amazing...