Chest minecart's entity light is rendered same as the player's entity light.That means if your body looks dark, you will notice that the chest minecart looks dark too.

Steps to reproduce:

1.go to an open area and place a chest minecart.

2.Cover yourself with tinted glass. (it will make you look dark)

3.look at the chest minecart outside.

Expected results:

the chest minecart looks bright because it's placed outside. /the chest minecart has its own entity lighting.

Observed results:

the chest minecart looks dark, the same as the player.