First three columns of launcher log are displayed darker than they were previously

The bug

The first three columns of the launcher log are displayed darker than they were previously. In older versions, the text in all four columns was white. Now, the first three columns are black:

How to reproduce

1. Start Minecraft using 2.2.2530 (haven't tested in other beta versions)
2. View the output log, and expand your window if necessary
   The text in the first three columns is black

Relates to MCL-17432.