Short answer
Paint is an alchemy brew from any one or two ingredients whose runes add up to exactly 2 green. Swamp mushroom, Flour or a bronze Onion each do it alone. The formula is a 20 red, 20 green technology, but the quest Safe Harbor gives it for free. The Trademaster and the Alchemist sell it, and it goes into Printed Money, Church Shrine III and the Safe Harbor hand-in.

The Astrologer's Tower
View full-size image ↗Official promotional screenshot · © Lazy Bear Games / tinyBuild · Official media kit · Material credits
The rune rule and mixes
Target: 2 green, nothing else. 21 combinations work on Laboratory I; each brew uses 1 Alchemy Flask.
One ingredient: Swamp mushroom, Flour, Onion (bronze) or Alchemic Powder (2 green).
Two ingredients: any two 1-green items, such as Berry + Leaf or Stick + Water.
Unlocking the formula
The Paint technology sits in column 6 of the Anatomy and Alchemy tree: 20 red and 20 green tech points.
The quest Safe Harbor grants it for free, so you may not need to spend the points.
As with every formula, brewing the right runes once also writes it into your Folio.
Where to buy and sell
Base price 2 silver. The Trademaster sells 10 from the start at about 5 silver; the Alchemist sells 5 / 10 / 10 by level.
The Trademaster buys it back for about 2 silver and the Alchemist for about 1 silver 50 bronze, plus weekly Likes. The Furniture Maker buys it from trader level 3.
What Paint is used for
Printed Money: 10 Clean Paper + 1 Paint at the Printing Press makes 10 Printed Money (Book writing mastery 4). The quest Press for Cash takes 20 of them.
Church Shrine III: one Paint in the building cost.
Safe Harbor: handed over for the quest.
Its blue twin is Lacquer (2 blue), which makes Live Bait and goes into Confession Booth III.

The Town from the official media kit. Paint goes into Printed Money and Town quests; this is not the Printing Press.
View full-size image ↗Official promotional screenshot · © Lazy Bear Games / tinyBuild · Official media kit · Material credits
Sources
- communitywikily.gg — Paint (item)
- communitywikily.gg — Paint (technology)
- communitywikily.gg — Printed Money
- communitywikily.gg — Lacquer
Related pages
Official screenshot · © Lazy Bear Games / tinyBuildAutomationGraveyard Keeper 2 Alchemy Guide
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Official screenshot · © Lazy Bear Games / tinyBuildCraftingGraveyard Keeper 2 Writing Desk
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Official screenshot · © Lazy Bear Games / tinyBuildThe TownThe Town in Graveyard Keeper 2