blue_sky vs sky

Is the blue_sky tag needed? 32 posts as of writing this message.

There is already night_sky, so one could assume plain sky generally refers to blue sky. True, there are exceptions, such as post #815649.

Options:

1. Alias blue_sky → sky would slow down "tag inflation".

2. Implication blue_sky → sky would call for a massive blue_sky tagging operation and, that completed, enable searches like sky -blue_sky -night_sky for those who want to find orange or gray skies.

3. Other?

Discuss.

I personally like the blue_sky tag and search for it, so No.2.

I'm fine with solution #2. Doing the implication now as it doesn't hurt anything.