In order to help with the transition from the brew command to the craft command in the creation of cures and poisons this post will cover issues that came up during development and decisions that had to be made.
What Was Before
The brew command works off of two values found on 'herb' items (leaves, roots, berries), their taste and color (referred to by players as 'tint vision', not to be confused with what appears in the sdesc or keywords). When providing the brew command with these items checks are made against a matrix of valid recipes.
An accepted combination of tastes apply a given poison or cure to the produced tablet (or vial). The color of the tablet is selected randomly from the color of the ingredients. Combining a blue and red herb will produce a blue OR red tablet. Combining a blue, red, yellow herb will produce a blue, red, OR yellow tablet.
In this way the color of the tablet has only a loose association with what the tablet does.
As a result of confusion on our part items built over the years, having not had this knowledge available, some saved versions of tablets have cures and poisons on them. This means that when some colors of tablet are produced they will have a cure-poison on them even if the tastes of the provided herbs were not a valid recipe. This falsely gives the impression that color is directed tied to purpose.
And, so, some of the standard recipes used by players are, in fact, bugs. Bugs that aren't present in the new system, meaning some cures and poisons will need further investigation when creating items from the brew command goes away.
What Is Now
The craft system is similar to brew in that the color and taste of herbs are taken into account. The first major difference is that colors are combined, where possible, rather than chosen from randomly. Combining a blue and red herb will produce a purple product - not a blue OR red product. When combining herb colors that don't mix well 'gray' is produced, instead.
The produced item from crafting cures no longer have values saved on them - which means only the valid recipes from the legacy system are maintained. The recipes being based entirely on combining the correct tastes. This is the second major difference and probably most notable because it will impact which cures players were able to make under the old system but not the new one. Please keep in mind that cures and poisons are still craftable but will require some experimentation to find the right combinations rather than being the result of bugs.
The final major change is that crafting herbs does not directly produce a vial or a tablet. Instead a 'mash' item is produced (or a globule, lump, powder, etc...) of the correct color. This item can either be consumed (with the eat command) directly to get the benefit from the cure or further crafted. Crafting it into a tablet can be done without more ingredients. If a vial is included then a vial with a cure is produced.
A change in this code related to vials is that they no longer disappear when they are used. Drink, pour, or use the vial and you will be left with an empty vial. This empty vial can be used to hold more cures. This system also allows any valid vial object to be used rather than one vial that must be used universally. Different regions and clans will have (hopefully) their own vials allowing characters to come up with their own system for which vial has which cure in it.
Likewise the color/taste system, now fixed in the new system, will allow characters to pick which 'acidic' herb they want to use in a recipe based on its color so that they can control the outcome. Yellow may have cultural references for one character that makes it obvious it is a cure for bloodburn, while another culture may view Yellow as the intuitive color for a poison, not a cure.