For water, see MC-201151.
The colour used for grass blocks on maps is constant and does not at all change even when crossing into other biomes. Vexingly this color appears to be the same as the alpha grass, meaning that the color maps use for grass is well over a decade out of date.
Foliage (trees, etc.) is affected similarly, and is also just as outdated.
This bug is not present at all in Bedrock Edition, and as such maps respect biomes. The following is an example with savanna, plains and forest biomes visible:
[media]Linked issues
is duplicated by 4
relates to 11
MC-201333
Dark prismarine, stairs or slab and prismarine, stairs or slab have wrong color on maps
Open
MC-201332
Normal shulker box and purple shulker box have wrong color on maps
Open
MC-174861
Waterlogged blocks are not accounted for when calculating water depth for map rendering purposes
Open
MC-201152
Melon and pumpkin stems appear green on maps regardless of growth stage
Open
MC-165776
Wood has different color than rotated log on map
Open
Attachments
Comments 16
Note that this bug does not exist on Bedrock Edition, and as such Bedrock Edition can be used as a model for the behaviour expected on Java Edition:
[media]
This may be intentional, as maps were added far after the old grass color phased out. The feature may be intentionally 'Bedrock Exclusive'.
This issue can be fixed easily, I did it once for a MC mod myself, don't know why developers are not interested in this. It adds much value to the game if the different biomes also show up differently on a map. Please Mojang? 🙂