Based on the screenshots it appears you are only painting using 20 colors. Please make sure you have uninstalled the non-PRO version and installed the PRO setup package. Also, go to Options | Painting and make sure the 'Improve paintings by utilizing different brush opacities' option is checked. Let me know! Thanks.
Viewing post in 100 colours is extremely dark
Great, now lets check the Palette Manager. Before painting, right click on the image and choose Manage Palette | Palette Manager from the context menu. You should see 100 colors in the list box. Let me know if this is the case. Also, have you tried any other images? Not sure if this issue is some-how isolated to this particular image. Thanks.