Hello!
Thank you for using my packs. I actually have an idea on how to prevent this from happening. You can use the black outline blocks and changing the colors to a darker version. For the grass block, you can color the top a darker shade of green and the bottom a darker shade of brown.
I am interested in adding a new update since this also occured to me while playing around with the tileset. For now, you will have to do the color switches manually until I manage to squeeze some time to update the packs.
My apologies,
Admurin