The commands I use for matching layers with each other is under Enhance Photo in the main menu strip atop the Editor. Clicking it will show a drop-down menu with a.o. Smart Photo Fix and Colour Balance.
Smart Photo Fix allows you to alter a layer for Brightness (with sliders for Overall, Shadows and Highlights), Saturation (with a slider for Less or More Colourfull) and Focus (with a slider fo Original to Sharper.
Colour Balnce using Advance Options show a first section called Optional Fine Tune with Temperature (with a slider for Cool and Warm) and Tint (with a slider for Purple and Green) and then a section called Enhance Color Balance with Temparature (with a slider Cooler and Warmer) and Tint (with a slider Purple and Green).
Every slider, when opened, show a preview with two panes, showing the original condition and the condition after you have moved a slider. Thes panes are called Before and After. You must check the little Preview on Image box, to be able to see the changes in the whole document.
Note that in the working space I have a document, that consists of a Background and one or more layers. Each layer contains a part of the total picture that I am composing. These layers may come from various other documents, in which I selected the specific part I need, so the layers in the document at hand will typically all have different contrasts, colour saturation and tints. To amalgate my document, all these layers must match each other in tint, colour and contrast, so that when all are merged, it is a coherent picture.
To do that, you need to see the panes of change in the commands together with the main document and all of its layers. In X-3 you can see that combination (Document in workspace, the layers palette with all the layers, and the command that I am using (such as Cooler and Warmer)). In X-6 that I once tried, with one of the commands as described above, such as Cooler and Warmer, you do not see the workspace any more, it is replaced by a full screen showing the pane with Before and After. So, X-6 is useless for this sort of matching to produce a coherent picture, and I think all subsequent PSP programmes are dito. Am I right?
I hope this makes any sense.