Simply maps do not reflect biome grass colours. I get that the map can only display blocks as they are in the world and grass blocks only have one colour table.
If this is intended, I would like the different grass colours that appear in biomes, to appear on the map as well.
It is very misleading and should be patched/implemented.
Thank you for your report!
We're actually already tracking this issue in MC-130658, so I resolved and linked this ticket as a duplicate.
If you would like to add a vote and any extra information to the main ticket it would be appreciated.
If you haven't already, you might like to make use of the search feature in the future to see if the issue has already been reported.
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