Getting the best from old photos
The colouriser is only as good as what you feed it. A few minutes of prep on an old photograph noticeably improves the result, because the model reads texture and tone to decide colour — and dust, low contrast and skew all confuse those cues.
Before you colourise
Scan or photograph it cleanly. A flat, evenly lit copy beats a phone snap at an angle. Crop to the photo — trim the album page, border or background so the model isn't colouring the mount. Fix contrast if it's very faded: a photo that's all mid-grey gives the network little to work with, whereas restoring a proper black point and white point brings back the texture it keys off. Straighten a skewed scan. You don't need to restore scratches for colour to work, but a cleaner brightness channel means cleaner colour.
Set the right expectations
Colourisation is interpretation, not time travel. The model produces plausible colour, not the true historical colour it can't possibly know — a grey dress might come out blue or beige, and it'll pick a reasonable skin tone rather than the exact one. Faces, skies, greenery and wood usually look right; brightly coloured or unusual objects are its best guess. Treat the output as a beautiful, believable interpretation — and if one region looks off, that's the nature of the problem, not a bug. Because the whole thing runs on your device, you can try several scans and crops freely, comparing with the before/after slider until one feels right, without uploading a single version.