I'm not finding the options for lightening/darkening tools. I'm sure they are in the "EDITOR" but under what heading or name? Not very interesting, I know. But.....
Sorry, i'm not quite sure what you are referring to? Is it a particular preset? If so, what kind of preset, and the name and category it's in?
Ok. In the Paint Color Source control panel in the paint synthesizer Editor, there is an Offset control. Typically, setting it lower than 0 darkens the color, making it higher than 0 lightens the color.
It's actually offsetting whatever colorspace is setup in the Start Option popup. That defaults to Clip Lum, so for most paint presets it's going to do what you want. If the Start Option popup was set to one of the Hue or Analogous color options, then the offset would be adjusting the hue as opposed to the Luminance.
The Paint Color Source control panel has controls that adjust the coloring of the paint strokes. The Paint Color Modulation control panel adjust how the color of the paint stroke might be modulated as the stroke is drawn. So for adjusting the paint coloring, those are the 2 control panels to go to first.
There is an additional Fixed Colors control panel associated with paint color. It lets you set up 2 different fixed colors (fixed color 1 and fixed color 2), which can be set to be specific colors, or to track the source color as some kind of offset (like lighter than, or hue shifted, or opponent color, etc). The 2 Fixed Colors are available inside many paint synthesizer menus as options to select. So you could use them tracking the source color as liger and darker offset colors to build a lighting gradient inside of a paint nib for example.
Another option is to modify the coloring of your source image, and then load the modified source image as the source for painting. Depending on the characteristics of your source image, this might be a useful thing to do anyway. By manipulating the source image coloring or contrast, you can help better define the final color of your painting. You could also selectively enhance certain objects in the image or blur out the background, which again will oftentimes translate into a better final painting.
In the Interactive Adjust op mode, the Lum Adjust or Bias Gain Adjust effects in there can be used to quickly adjust the luminance of the canvas image, or adjust a variable non linear tone curve. To use the Interactive Adjust effects, you mouse down in the canvas and then move the mouse to adjust the effect. How you move the mouse horizontal or vertically from your mouse down position is going to adjust the interactive adjust effect.
I oftentimes add finishing steps after i am done painting or running some kind of effect process, to boost contrast and edge enhance the final canvas. The Image Compressor ip op effect is a really good one to use for finishing. It generates an adaptive contrast boost effect. So it can take a too dark or too light image and snap it back into optimal lighting.
I use the Blur ip op with the Edge 1 composite setting to sharpen the canvas. Changing the Composite setting can dramatically change an effect, in this case changing a Blur effect to a Sharpen effect. Changing the Blur Amount will control that spatial frequency of the sharpening effect. Setting it at 70 gives a good edge sharpen. Setting it at 99 gives an unsharp masking effects. I usually set the Mix % to 20% when doing sharpening, since a little bit goes a long ways.
I have a specific custom Favorites category i keep different finishing presets in, so i can quickly use them while working. So i usually clean up any too light or too dark paint issues in my finishing contrast boost steps.