We have a couple of instances of GeoServer running, one of which is the latest version and the other is version 2.1.3.

The older version has Ordnance Survey base mapping which is loaded as a number of EPSG:27700 image-mosaics. These are then reprojected by GeoServer into the Google projection EPSG:900913 and displayed as part of a layer group where the style switches the layers on / off depending on the scale. We believe this is a fairly standard use of GeoServer to provide a base map coverage and it works fine.

In the newest versions of GeoServer the same base map layer creates a horrible orange coloured map as it seems to be breaking the colour banding of the layers. Seems to be turning the large swaths of blue sea into orange, as well as screwing the colours on the rest of the map. I can't upload a screenshot as our organisations internet policies restrict it.

Please note, you need to reproject two image-mosaics and combine them in a layer group or GetMap to reproduce the error.

We wondered if anyone else has experienced the bug in the latest versions, and whether there are any solutions or workarounds anyone has come across.

2 Answers 2


Check if the source data uses paletted colours. You can not reproject them easily, because interpolating paletted colours will fail.

Convert the source data to RGB or RGBA, and the interpolation during reprojection will deliver good looking results.

Furthermore, check if NODATA value conflicts with any used colour.


The base dataset is in RGB format but the issue is caused when one layer is not visible due to Min/MaxScaleDominator in the SLD. If you check the two layers individually using GDALinfo I believe you will find that the format of the blank tile has been changed by GeoServer and is now RGBA whilst the visible tile is still in the original RGB.

We think it is the combining of RGB and RGBA tiles which causes the issue.

Also, please note that the reprojected tiles are fine when viewed individually so it is unlikely to be an issue with the base datasets. It is only when you combine the two layers and one of them is invisible that the error occurs.

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