To change a layer, I use the menu Enhance Photo/Smart Photo Fix, where you can change light/dark and colour intensityper layer. Also in the same menu, there is Colour Balance, where you can make colours cooler or warmer, or change green/purple levels, also in each layer seperately.
See screen shots. The picture on the right is the original photo and I want to change the tone and colour of the seperate elements (i.e. river, tower, ship etc). So, I have layered the river, the tower, the ship and the trees, and set them on the background, i.e. the original photo. Now, I have first darkened the original pic, of which you only see the sky, the rest is covered by the layers, see left picture in the first screen shot. Next, I can change the the tower to a darker shade and I can compare it to the sky, see the left picture in the second screen shot. I use the sliders in the menu Smart Photo Fix. Note, that the Editor remains visible, so that the picture with the changing layers is fully and complete (layers-wise) visible.
In the later PSP programmes, you cannot do this: if you select a layer to change light or dark etc, the complete picture disappears, and the Editor shows only the layer that you are changing. You see what I mean? You cannot assess the changes in one layer with respect to the others. I discussed this earlier with Cassell, and she said, that Corel said “Too bad” , therefore my question is, did Corel put this property back in PSP 2018??