They are, the Next uses a palette of 256 from a total 512 available. I wonder if the converter was made from the old palette which was different before release.
Viewing post in DAAD Ready iffy graphics conversion
The way that this works is that Adventuron takes the image, allocates each new RGB combination to a palette slot. It uses up to 255 slots for 255 different colours (the next needs one colour for transparency).
After it runs out of 255 colours then colours are matched to the closes existing palette colour. That algorithm is pretty basic, and most people won't have to worry about running out of 255 colours in pixel art graphics.
From there, Adventuron converts the images to PCX image files (supports up to 256 colours palettized). There is no colour conversion during the PNG to PCX conversion (assuming < 256 colours).
DAAD Ready then uses a tool called "SC2DAAD" to convert the PCX file format to NXT file format. I assume that's where the mapping error is occurring. If there is a concrete example of the graphics being badly paletted then I'm sure Uto can take a look.
Chris
Tentatively good news.
I spoke to Uto.
He built his converter on the old ZX Next specs (with only 4 shades of blue).
I told him that you informed me that 9-bit colour is now available on the Next (max 256 out of 512 as you said).
It appears the export from adventuron doesn't require any changes (because I left palette allocation to the SC2DAAD utility which is part of DAAD Ready).
Anyway, Uto told me to say "tell him I found he is right, and I'm working on it".
Huge (huge) thank you to Uto for DAAD Ready / Maluva / SC2DAAD and the DRC compiler.
Fingers crossed.