Why do my Midjourney coloring pages print gray?

AI models output RGB images whose line edges are anti-aliased — a gradient of gray pixels rather than solid black — and often add faint shading even when you ask for none. On a printer those gray edges reproduce as a light, washed-out line instead of crisp black.

How do I make AI coloring lines pure black for KDP?

Convert the image to grayscale and push faint/gray strokes to solid pure-black while keeping each line's weight and detail, remove speckle, and render at 300 DPI for your trim. Prepressly does this automatically in the browser and exports a true DeviceGray PDF.

Does forcing lines black also increase resolution?

No. Blackening lines fixes the gray/faint problem but does not add real resolution to a small source image. Start from the largest export your AI tool allows. True AI upscaling is a separate step.

AI art → KDP · 한국어

AI coloring pages print gray on KDP — fix muddy lines to pure black

For sellers making coloring books from Midjourney, Stable Diffusion, Leonardo, or DALL·E. Updated 2026.

Your AI line art looks crisp black on screen, then prints light and gray in the KDP proof. This is the most common — and most fixable — problem with AI-generated coloring books. Here's exactly why it happens and how to correct it.

Why AI line art prints gray

Three things stack up:

Anti-aliasing. Every AI image is RGB, and the model draws smooth edges by fading each line into the white background across a few gray pixels. On screen that looks like a clean black line; on a printer those gray edges reproduce as a soft, washed-out stroke.
Residual shading. Even with prompts like "black and white line art, no shading, no color," models sneak in faint gray fills and gradients. "--no colors" in Midjourney reduces color but doesn't force pure black.
Compression + resizing. Saving as JPEG and resizing to fit an 8.5 × 11 page smears the edges further into mid-gray.

The result: lines that measure 40–70% gray instead of 100% black. Buyers see it and leave "the pages are too faint to color" reviews — or KDP's reviewers flag the interior quality.

Better prompting helps a little (ask for "thick clean solid black outlines, pure white background, high contrast, no gray, no shading"), but the export is still anti-aliased gray. You need a post step that forces the lines to solid black. That's the actual fix below.

The fix: force faint lines to solid pure-black

Export as large as your tool allows (Midjourney upscale, SD hires) — this can't add detail later, so start big.
Convert to grayscale and push every faint/gray stroke toward solid pure-black — while keeping each line's original weight and detail, so nothing gets thinned or dropped.
Remove speckle — the stray gray dots AI and scans leave in the "white" areas.
Render at 300 DPI for your trim and export as a true grayscale (DeviceGray) PDF, not RGB.

You can do steps 2–4 by hand in GIMP or Photoshop with Threshold/Levels, but a hard threshold tends to break faint lines and drop detail. Prepressly uses an adaptive method that darkens the faint strokes without thinning them.

Honesty check: forcing lines black fixes the gray problem. It does not invent resolution — if your source is genuinely small, the lines will be crisp and black but still soft where there was never detail. True AI upscaling of low-res art is a separate step (Prepressly's high-resolution AI enhance is coming soon).

One more thing: KDP's AI review in 2026

Amazon KDP asks you to disclose AI-generated content, and coloring / activity / low-content titles increasingly get a short manual review (often a few business days) before going live. Clean, high-contrast, correctly-formatted interiors clear that review faster than muddy ones — so fixing the lines helps twice.

Blacken your AI lines free, in your browser

Drop your AI pages in — Prepressly forces faint/gray lines to bold pure-black at 300 DPI, cleans speckle, fits your KDP trim, and exports one DeviceGray PDF. Nothing is uploaded.

Open Prepressly — free

Keep reading

Why KDP rejected your coloring book interior — fix each errorTrim, margins, gutter, DPI, bleed — the exact numbers. KDP trim, bleed & margin cheat-sheetPick a trim + page count → exact PDF size and margins.