The bug

Dark oak logs with a vertical orientation use the same map color as horizontal logs / dark oak wood blocks despite them having a different color on the top.

See also MC-165776

How to reproduce

1. /fill ~1 ~ ~1 ~6 ~ ~6 minecraft:dark_oak_log[axis=y]
   

2. /fill ~7 ~ ~7 ~12 ~ ~12 minecraft:dark_oak_log[axis=x]
   

3. Create a map
   The blocks have the same colors on the map despite them having different top textures