I think it will be easiest to explain on an example. Here is the screenshot from CustomJS plugin settings where I have no value in the top input (you can see a placeholder value instead) and I have value in the bottom one. Both input look similar, there is no easy way to tell that the upper one is just a placeholder without any real value:
Now take a look at a screenshot I made after adding my changes. Here placeholder uses way darker color:
I think it will be easiest to explain on an example. Here is the screenshot from CustomJS plugin settings where I have no value in the top input (you can see a placeholder value instead) and I have value in the bottom one. Both input look similar, there is no easy way to tell that the upper one is just a placeholder without any real value:
Now take a look at a screenshot I made after adding my changes. Here placeholder uses way darker color: