At what stage do leaves get darker ? This is confusing

They'll darken up as they get a little older... new growth is always a lighter shade of green. I AM seeing a bit of a potassium deficiency starting (edges of some of the leaves are getting brown) so you might want to add in a good PK booster which shouldn't raise your EC that much... I'm actually surprised she can't tolerate a higher EC at this point - but I think that's more of a reaction to what is comprising the EC rather than the actual reading.... in other words, if you had a lot of nitrogen in your nute solution versus reducing the nitrogen and pumping up the PK, she might not react badly to it at all... Just a thought - at least that's what I find in my DWC grows... Good luck!

They look pretty good to me. Dark leaves are usually a sign of a nutrient toxicity, so you don't want them to be too dark, or you may have problems. During the middle of flower is when they'll start showing their colors, if they have any colored genes in them that is. Like purples, blues, oranges, shades like that. I love watching plants fade. It's like going for a drive in the fall where i live. If you're new here, please select the answer that helped you out the most by clicking on the "answer" button underneath what the person said. If you have any questions, feel free to message me on here. You can pull up your messages tab by clicking on the little airplane in a bubble. It's located on the bottom-right of your screen. I hope this helps!

After they stop stretching the leaves tend to mature and get a bit darker. That is when I usually reduce the A and B and start to introduce some Potassium and phosphorus to help bud development.