A lot has changed about texture painting visualization with 2.8x. To see the general process demonstrated, I recommend this course and/or this livestream.
But more specifically, do you mean the “shadeless” mode where you’re only painting the pure color information?
While we figure this out it’s probably best if I can troubleshoot your .blend file. If you post a download link to your .blend file I’ll be happy to take a closer look. The best way to do this is by saving a version of your blend file after packing the textures with it by going to File > External Data > Pack all into .blend. Then upload your file to Dropbox, Google Drive, Mega, or equivalent file hosting service then copy + pasting the share link here.
