Is it possible to paint the icons in the panel by using the color directly underneath them? Sometimes you have pictures that are white on the right and dark on the the left and you can see only one side.
no this is not possible... this is why there is the busy flag for backgrounds when the background is automatically hidden when option "Hide background when not needed" is applied. If the background is too busy then in the previous case the background opacity is used in order to provide proper visibility.
Yes you are right. The problems is just that for automatic wallpaper changes Plasma uses a background color that Latte adjusts too.
I already asked for the Plasmashell team to change this btw. Hope they will implement it soon https://bugs.kde.org/show_bug.cgi?id=431735