Yes sure, we are here to help.
Main_pager means main menu's pager (arrow) bitmap background. Since you want to change the pager appearance for the submenu, you should change Submenu_pager. If it is a number, for example, if Submenu_pager=5 then it means the resource number 5 under 'Bitmap' in Resource Hacker is the background bitmap for the submenu. Replace it with another modified bitmap with the colors of your choice and correct dimensions and you will have the background changed.
Because in your case, the submenu is a slightly greyish black, black separators would suit it. So prepare a black background image of the same dimensions. So select the correct submenu_pager_arrow bitmap and replace it with another one using Resource Hacker's Action menu.
As for the pager arrows, you need them white or some other color if background is black, otherwise they won't be visible.
Feel free to ask if you have difficulty. You can also upload your skin file here and tell us what color you want the pager arrows and pager arrow background to be.
Oh and the bitmap needs to be a 32-bit bitmap (24-bit with transparency, so make sure your replacement bitmap is made with the correct editor.
Step by step would go somewhat like this (Make sure you are running Resource Hacker as administrator if you are editing a skin file located in C:\Program Files\Classic Shell\Skins\ or another UAC protected directory):
1. Open the skin file in Resource Hacker and find what submenu_bitmap says in the skin.
2. Go to that number under "Bitmap" in Resource hacker.
3. Save it by right clicking it.
4. Open it in your favorite bitmap editor like Photoshop or GIMP.
5. Change the colors to what you want.
6. Save the bmp as a 32-bit bmp
7. Make sure the bitmap to be replaced is again selected in Resource Hacker and then from Action menu, click Replace bitmap.
8. Browse to the modified one and click Replace.
9. Better to exit Classic Shell before saving to avoid an access violation error.
10. Save the skin file and start Classic Shell again.