So this tool now exists. But unlike colour constructor, there is a fairly steep learning curve to this program, which requires a more indepth knowledge of light to get the most out of it. But also learning how to use this tool will increase your understanding of light, so the learning curve is actually not a bad thing.
Lets get into it.
Assuming you managed to follow the read me and have Prisma Palette up on screen, we are going to set up some basic lights and learn how to use them to manipulate colours.
The first step is to make sure that we have two lights in the scene. if you have too many, hit edit on the undesired light and hit delete. If you are missing them, make sure you are in lit mode, and then press the + Light button to add a light.
Now with this setup. You set your shadow colours by only having the ambient light on. any colour you pick from the picker will now be a shadow colour. If you have the key light on as well as ambient, these are your lit colours. Variance in gamuts will come from the settings that you give these lights and the relationships the lights have to each other.
The next thing we will look at is how to set the light values to get the best results. Perhaps the most counter intiative aspect to this approach to colours is that for most situations, the ambient light will need to be set brighter than the lit colour.
If we sit down and think about it we can work it out though. Lights are additive, meaning that everytime we turn on another light, both of these add together. If you want things to still be visible in the shadows, you need to have a fairly bright ambient to do that, but then when it comes to a direct light, it's how much brighter we want it that defines what value it should be.
The other major consideration for picking lights is one of exposure. We are painting within a limited value range, but with additive lights, it's very easy to break outside of that range and blow out the lights. Blowing out the lights is no good because the reverse engineering of local colour completly breaks and Prisma Palette is unable to work properly(it also looks... questionable, but that's up to artistic taste). In order to prevent this, i recommend setting your ambient light to the brightness that you want your shadows, and then setting your key light to as bright as you can set it without the overexposure warning going off.
local Colour Picking.
Unlike Colour Constructor, Prisma Palette lacks a feature to save objects. This is intentional, because we are able to reverse engineer local colours assuming that we colour pick using the identical light settings to when you painted the colour. This means that if you have your shadow settings on, you can pick a shadow colour, turn on the key light and it will generate the lit colour again.
This functionality will not interfere with normal photoshop functionality and you can ignore what the panel is doing until you need it again. The panel will only construct the new colour when the local colour is changed, or when lights are switched on/off/modified.
However picking a colour in the wrong mode and attempting to convert the colour will cause incorrect behaviour.
Light Layers and Shortcut
Prisma Palette includes a script in the install to allow for a shortcut key to be bound to switching through lights.
To set this up, go to the edit menu -> keyboard shortcuts. Once in shortcuts go to application menus, and open file and scroll down to scripts. You should find a a script called PrismaPanelShortcut. Assign this to a key. One limitation of this method of setting a shortcut means that you must assign it to a ctrl+other key or a f button. I chose to put it on f2 for convinience.
This shortcut controls the cycle through lights, turning them on and off according to the numbered toggles at the bottom of each lights settings. Setting a light to 1 will cause it to turn on at one in the light layer cycle.
The cycle can be incremented by the number next to add light.
This tutorial will be expanded soon.