What is the ACB file format?
.acb is a settings file format used by Adobe Photoshop and related Adobe applications. .acb files store named spot-color swatches in the form of records that together comprise a color book. Each record corresponds to a single color and carries attributes including a name, reference code, color model (RGB, CMYK, or Lab), and per-channel component values. .acb files also contain a header section with the book title, a unique book identifier, color-name prefix and suffix strings, page size for the picker display, and the total record count.
The format is identified by the four-byte binary signature 8BCB (hex: 38 42 43 42) at the start of the file.
Color books are used for standardizing spot-color selections across print and design projects - Pantone, HKS, TOYO, and DIC Color Guide libraries are all distributed as .acb files with Photoshop. CMYK-based books target print workflows, while RGB books suit screen-oriented work. Default .acb files are stored in the Presets/Color Books subfolder of the Photoshop installation and appear automatically in the Color Libraries panel of the Color Picker.
Although .acb has not been formally superseded, the newer .ase (Adobe Swatch Exchange) format is preferred for sharing general-purpose swatches across Adobe applications. Photoshop continues to load .acb color books for named spot-color workflows such as Pantone matching.
Security & safety
RISK: LOWACB files contain only color definitions - no executable code or scripts - so they are low risk. The only caution is sourcing: download color books from reputable vendors, since a corrupt or malformed book can fail to load in Photoshop. Pantone licensing changed in 2022 (Pantone libraries were removed from Adobe's bundled set), so third-party PANTONE .acb files circulate online; verify the source for accuracy rather than for malware.
Format details
in a nutshell- Microsoft Access Compiled Module / project (legacy) - Some old Access tooling produced .acb compiled-module files; unrelated to color books.
- CRI Middleware ACB audio cue sheet (game audio) - Game engines (CRI ADX2) use .acb as an audio cue-sheet container paired with .awb; a different binary format entirely.
Programs that open ACB files
Windows3 apps
Adobe Photoshop
Paid Place the .acb in Presets/Color Books, restart Photoshop, then open the Color Picker → Color Libraries to select the book. 
Adobe Illustrator
Paid Swatches panel → menu → Open Swatch Library → load color book from Presets/Color Books. 
macOS2 apps
Adobe Photoshop
Paid Copy the .acb into Presets/Color Books inside the Photoshop app folder, restart, pick it in Color Libraries. Technical details
deep spec| Magic bytes | 8BCB (hex: 38 42 43 42) at offset 0 - Adobe Color Book binary signature |
| Byte order | Big-endian |
| String encoding | UTF-16 Big-Endian, Pascal-style length-prefixed (2-byte length field + UTF-16 characters) |
| Color models | RGB, CMYK, or Lab (L*a*b*) - one color model per book; components stored as scaled integer values |
| Color record fields | Name string, reference code string, per-channel color component values |
| Header fields | Version (16-bit), book ID (16-bit), title, color-name prefix, color-name suffix, page size, color space, color count |
| Version field | 16-bit big-endian integer; value = 1 for all known published Adobe color books |
| Typical file size | 2 KB-200 KB (a few dozen to several thousand named color entries) |
| Storage location | Presets/Color Books/ subfolder within the Adobe Photoshop installation directory |
| Access in Photoshop | Color Picker → Color Libraries button; books appear as a named drop-down library list |
| Example libraries | PANTONE, HKS, TOYO, DIC Color Guide - all shipped as .acb files with Photoshop |
| Cross-app support | Loadable in Adobe Photoshop, InDesign, and Illustrator; not supported in non-Adobe applications |
| Released | Late 1990s (with Photoshop's named color books / Pantone libraries) |
| Latest version | ACB version 1 (16-bit version field; unchanged for years) |
| Specification | ates.dev |
ACB conversions
Community Q&A
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