Signs facing south or north have slightly darker colors

What I expected to happen was...:
Sign colors should always stay the same, the brightness shouldn't change

What actually happened was...:
Signs facing south and north have slightly darker colors, for example white turns into grey, aqua into dark aqua.

Steps to Reproduce:
1. Get signs with colored text, try this:
/give @p sign 1 0 {BlockEntityTag:{Text1:"{\"text\":\"\",\"extra\":[{\"text\":\"===============\",\"color\":\"white\"}]}",Text2:"{\"text\":\"\",\"extra\":[{\"text\":\" Test Text\",\"color\":\"aqua\"}]}",Text3:"{\"text\":\"\",\"extra\":[{\"text\":\"Text Test\",\"color\":\"green\"}]}",Text4:"{\"text\":\"\",\"extra\":[{\"text\":\"===============\",\"color\":\"white\"}]}",id:"Sign"}}

2. Place one sign (or more) facing west or east, and one (or more) facing south or north

3. See the difference? It's really annoying...

I don't actually know if you can see the colors on the signs on the picture I attached... Let me just hope so