How is your SEO going to get green?

So far 149 images out of 1251..............11.9%

I wished there was a plugin for this!

Zero. I am not getting further than orange and yellow, which is fine for me

It's actually all explained in the Yoast SEO section.
Once you've set a focus keyword, all you have to do is mention it a couple of times in your title, page heading, meta description, URL and in your over 300 words page description. Piece of cake. 

Mainly yellow for me as well. Only a few in the green when i can find some better descriptive text for e.g. plants and such. Google's keyword search is really a great help and at times an eye opener = suggestions for focus keywords i couldn't think of but where right in front of my nose.

Agree with Mark. I wish there was an automatic script or plugin doing all that for me.