Not sure what this is.

Are you using RO water? It looks like a deficiency macro nutrients like calcium.

Calcium deficiency developing.

Its just an abnormalitie. The plants pigment early on, like newborns pigment develops with contact with environmental conditions.. As its so uniformed and the plant overall looks very healthy. I'm sure not what your ppm is. But, if you've it set at 400 and the ppm is going up. There's too much water intake. With DWC you shouldn't have big swings in EC/RH up/down. So, it might be a slight sign you need to do these checks. And after a few hrs if your EC is similar to what it was when u put on hrs earlier then you've got it right. The PH swings happen early on. As the water lowers the ph buffers in the nutrients the PH buffer will either have up or down this just needs to be adjusted but a good set DWC tank you shouldn't have to adjust the EC (swings without 50-70 up/down is fine) There's lots of ways ppl tackle their DWC. like when levels go down they just add a smaller quantity of what they started with (nute mix wise) and if the plant stays within a short EC drop/rise then you'll know. You'll need a good solution EC pen. I've had my Millwall 2yrs and it always gives me my correct EC with my CONTROLLED PH / EC buffers for cal for pens. So, id suggest investing in a good PH/EC pen. Ph55/ec60 milkwalkuee is like 100euro. Really good.

Most likely this is nothing to worry about at this stage of growth. The discoloration is most likely due to excessive water retention. If that's the case your plant will grow out of it naturally. I use any water soluble agricultural or horticultural grade kelp or kelp meal amendment for a fix. The inclusion of Vitamin B1 is the key here. It will help with both water uptake regulation and nutrient absorption. If it's not a water regulation issue it might be pH or a subtle lockout of a micro element. But, it probably isn't that if you know your pH is on par and all major and minor elements are available to your plant its root zone. Plant looks fine otherwise. Indoors you should love to grow hydro. Although people are still trying to figure out how to universally grow indoor cannabis in soil without all the issues attached to that method -- they'll come around over time. Dig in deep, keep the expenses down to the absolute minimums, and enjoy fine top shelf cannabis that your can repeat with success time after time after time. Good luck!

Most likely this is nothing to worry about at this stage of growth. The discoloration is most likely due to excessive water retention. If that's the case your plant will grow out of it naturally. I use any water soluble agricultural or horticultural grade kelp or kelp meal amendment for a fix. The inclusion of Vitamin B1 is the key here. It will help with both water uptake regulation and nutrient absorption. If it's not a water regulation issue it might be pH or a subtle lockout of a micro element. But, it probably isn't that if you know your pH is on par and all major and minor elements are available to your plant its root zone. Plant looks fine otherwise. Indoors you should love to grow hydro. Although people are still trying to figure out how to universally grow indoor cannabis in soil without all the issues attached to that method -- they'll come around over time. Dig in deep, keep the expenses down to the absolute minimums, and enjoy fine top shelf cannabis that your can repeat with success time after time after time. Good luck!

Check your pH make sure your in the right range. Looks like you are getting a Manganese deficiency. Best of luck the rest of the way!