I am using Linux Mint 19.2 Tina Cinnamon. I installed the Dolphin file manager because I like having the split panes. Plus Dolphin has lots of other options that I like. Anyways, I have played with the settings and I have most everything as I like it, except that in Dolphin, the background where the files and folders are, is white, which makes it hard to see my files and folders unless I select them. I would like to know how I can change the white color to something else. Will someone please help me?

In KDE that's usually accomplished by editing the system (qt) color scheme via KDE's System Settings -> Colors, select the color scheme you want to edit and hit Edit Scheme. In that dialog, select Color set: View, then change the Normal Background to your liking, Normal Text (and other text colors) to provide sufficient contrast and Alternate Background color to something similar to the Normal Background (for alternate rows when using dolphin's Detail view mode).

I'm not sure how to change those using other graphical tools; but you can find the files for those schemes under /usr/share/color-schemes and ~/.local/share/color-schemes. The colors to change will be in the [Colors:View] section.